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Prokaryotic transcriptionFrom Wikipedia, the free encyclopedia

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Prokaryotic transcription is the process in whichmessenger RNAtranscripts of genetic material

inprokaryotesare produced, to be translated for the production ofproteins. Prokaryotic transcription occurs

in thecytoplasmalongsidetranslation. Unlike ineukaryotes, prokaryotic transcription and translation can

occur simultaneously. This is impossible in eukaryotes, where transcription occurs in a membrane-bound

nucleus while translation occurs outside the nucleus in the cytoplasm. In prokaryotes genetic material is not

enclosed in a membrane-enclosed nucleus and has access toribosomesin the cytoplasm.[1]

Transcription is known to be controlled by a variety of regulators in prokaryotes. Many of these transcription

factors are homodimers containing helix-turn-helix DNA-binding motifs.[2]

Contents

[hide]

1 Initiation

2 Elongation

3 Termination

4 References

5 External links

[edit]Initiation

The following steps occur, in order, for transcription initiation:

RNA polymerase (RNAP) binds to one of several specificity factors,, to form aholoenzyme. In this

form, it can recognize and bind to specificpromoterregions in the DNA. The -35 region and the -10

("Pribnow box") region comprise the basic prokaryoticpromoter, and |T| stands for theterminator. The

DNA on the template strand between the +1 site and the terminator is transcribed into RNA, which is

thentranslatedintoprotein.At this stage, the DNA is double-stranded ("closed"). This

holoenzyme/wound-DNA structure is referred to as the closed complex.

The DNA is unwound and becomes single-stranded ("open") in the vicinity of the initiation site (defined

as +1). This holoenzyme/unwound-DNA structure is called the open complex.

The RNA polymerase transcribes the DNA (the beta subunit initiates the synthesis), but produces

about 10 abortive (short, non-productive) transcripts which are unable to leave the RNA polymerase

because the exit channel is blocked by the -factor. The -factor eventually dissociates from the holoenzyme, and elongation proceeds.
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er_(biology)http://en.wikipedia.org/wiki/Holoenzymehttp://en.wikipedia.org/wiki/Sigma_factorhttp://en.wikipedia.org/wiki/RNAPhttp://en.wikipedia.org/w/index.php?title=Prokaryotic_transcription&action=edit&section=1http://en.wikipedia.org/wiki/Prokaryotic_transcription#External_linkshttp://en.wikipedia.org/wiki/Prokaryotic_transcription#Referenceshttp://en.wikipedia.org/wiki/Prokaryotic_transcription#Terminationhttp://en.wikipedia.org/wiki/Prokaryotic_transcription#Elongationhttp://en.wikipedia.org/wiki/Prokaryotic_transcription#Initiationhttp://en.wikipedia.org/wiki/Prokaryotic_transcriptionhttp://en.wikipedia.org/wiki/Prokaryotic_transcription#cite_note-1http://en.wikipedia.org/wiki/Prokaryotic_transcription#cite_note-0http://en.wikipedia.org/wiki/Ribosomehttp://en.wikipedia.org/wiki/Eukaryoteshttp://en.wikipedia.org/wiki/Prokaryotic_translationhttp://en.wikipedia.org/wiki/Cytoplasmhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Prokaryotehttp://en.wikipedia.org/wiki/Messenger_RNAhttp://en.wikipedia.org/wiki/Wikipedia:Verifiability#Burden_of_evidencehttp://en.wikipedia.org/wiki/Template:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Identifying_reliable_sourceshttp://en.wikipedia.org/w/index.php?title=Prokaryotic_transcription&action=edithttp://en.wikipedia.org/w/index.php?title=Prokaryotic_transcription&action=edithttp://en.wikipedia.org/wiki/Wikipedia:Verifiabilityhttp://en.wikipedia.org/wiki/Wikipedia:Citing_sources#Inline_citations


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[edit]Elongation

Promoters can differ in "strength"; that is, how actively they promote transcription of their adjacent DNA

sequence. Promoter strength is in many (but not all) cases, a matter of how tightly RNA polymerase and its

associated accessory proteins bind to their respective DNA sequences. The more similar the sequences

are to aconsensus sequence, the stronger the binding is. Additional transcription regulation comes

fromtranscription factorsthat can affect the stability of the holoenzyme structure at initiation.

Most transcripts originate using adenosine-5'-triphosphate (ATP) and, to a lesser extent, guanosine-5'-

triphosphate (GTP)(purinenucleoside triphosphates) at the +1 site. Uridine-5'-triphosphate (UTP) and

cytidine-5'-triphosphate (CTP)(pyrimidinenucleoside triphosphates) are disfavoured at the initiation site.

[edit]Termination

Two termination mechanisms are well known:

Intrinsic termination (also calledRho-independent transcription termination) involves terminator

sequences within the RNA that signal the RNA polymerase to stop. The terminator sequence is usually

apalindromicsequence that forms a stem-loophairpinstructure that leads to the dissociation of the

RNAP from the DNA template.

Rho-dependent termination uses atermination factorcalled factor(rho factor) which is a protein to

stop RNA synthesis at specific sites. This protein binds at a rho utilisation site on the nascent RNA

strand and runs along the mRNA towards the RNAP. A stem loop structure upstream of the terminator

region pauses the RNAP, when -factor reaches the RNAP, it causes RNAP to dissociate from the

DNA, terminating transcription.

[edit]References

o fully understand transcription, students need to appreciate the dynamic nature of this process. Transcription"works" because nucleotides diffuse into position from the cytoplasm, the DNA helix unwinds and then rewinds,

and the RNA polymerase travels rapidly along a DNA template strand for hundreds or thousands of bases toproduce a very long RNA molecule in its wake. This simple, 40-s animation is presented at three levels ofmagnification to emphasize the movements of all the players.

At the beginning of the animation, an RNA polymerase (RNAP) is shown binding to the promoter region of adouble helix of DNA. The sigma subunit of RNAP helps to locate the promoter, after which it is no longerneeded.

Then, as we look "inside" the RNAP, we can see that the double helix begins to unwind. A growing strand ofRNA (in red) begins to form along one of the DNA strands. As the strand lengthens, the RNAP continues totravel along the DNA, unwinding it to expose more DNA bases. Behind the RNAP the DNA helix reforms,displacing the RNA strand.

Finally, we zoom in further to the active site of the RNAP molecule. Here, we can see how an RNA nucleotidetriphosphate (in this case, an "A," for a ribose triphosphate with an adenine base) diffuses into position andbinds to its complement a "T" on the DNA strand (note that the blue deoxyriboses on the DNA strand have

the opposite orientation to the red ribose residues on the the RNA strand). Once hydrogen bonding haspositioned the "A" and the "T" together, the RNAP is able to catalyze covalent bonding of the "A" to the 3-OHon the growing RNA strand. This bond formation is powered by the cleavage of the diphosphate from the RNA
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nucleotide. The process is quickly repeated as another RNA nucleotide triphosphate, "C," is added to the RNAchain. Moments later, a DNA nucleotidea "T"diffuses into position. While this nucleotide can hydrogen bondwith the "A" on the DNA template strand, the RNAP discriminates between RNA and DNA nucleotides, and noreaction is catalyzed. Ultimately, the deoxyribonucleotide diffuses away, allowing RNA strand synthesis tocontinue when another ribonucleotide triphosphatea "U"hydrogen bonds with the A on the DNA templatestrand.


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Concept 2: Transcription and Translation in CellsIn a prokaryotic cell, transcription and translation are coupled; that is, translation

begins while the mRNA is still being synthesized. In a eukaryotic cell, transcription

occurs in the nucleus, and translation occurs in the cytoplasm.Prokaryotic Cell

Because there is no nucleus to separate the processes of transcription and translation, when

bacterial genes are transcribed, their transcripts can immediately be translated.Eukaryotic Cell


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Transcription and translation are spatially and temporally separated in eukaryotic cells; that is,transcription occurs in the nucleus to produce a pre-mRNA molecule.

The pre-mRNA is typically processed to produce the mature mRNA, which exits the nucleus and istranslated in the cytoplasm.

Concept 3: Different Genes for Different RNAsThere are 4 types of RNA, each encoded by its own type of gene.The genomic DNA contains all the information for the structure and function of an organism.

In any cell, only some of the genes are expressed, that is, transcribed into RNA.

There are 4 types of RNA, each encoded by its own type of gene: mRNA - Messenger RNA: Encodes amino acid sequence of a polypeptide.

tRNA - Transfer RNA: Brings amino acids to ribosomes during translation.

rRNA - Ribosomal RNA: With ribosomal proteins, makes up the ribosomes, the organelles thattranslate the mRNA.

snRNA - Small nuclear RNA: With proteins, forms complexes that are used in RNA processing ineukaryotes. (Not found in prokaryotes.)


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Concept 4: Basic Structure of a Protein-Coding Gene

A protein-coding gene consists of a promoter followed by the coding sequence for the

protein and then a terminator.

The promoter is a base-pair sequence that specifies where transcription begins.

The coding sequence is a base-pair sequence that includes coding information for the polypeptidechain specified by the gene.

The terminator is a sequence that specifies the end of the mRNA transcript.

Concept 6: The Transcription ProcessRNA synthesis involves separation of the DNA strands and synthesis of an RNA moleculein the 5' to 3' direction by RNA polymerase, using one of the DNA strands as a template. In complementary base pairing, A, T, G, and C on the template DNA strand specify U, A, C, and G,respectively, on the RNA strand being synthesized.

Concept 7:

Complete Transcription of an RNA Molecule

Transcription begins at the promoter, proceeds through the coding region, and ends at

the terminator.

Concept 8: mRNA in Prokaryotes

The sequence of a prokaryotic protein-coding gene is colinear with the translated mRNA;

that is, the transcript of the gene is the molecule that is translated into the polypeptide.
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mRNA in Eukaryotes

The sequence of a eukaryotic protein-coding gene is typically not colinear with the

translated mRNA; that is, the transcript of the gene is a molecule that must be

processed to remove extra sequences (introns) before it is translated into thepolypeptide.

Most eukaryotic protein-coding genes contain segments called introns, which break up the aminoacid coding sequence into segments called exons.

The transcript of these genes is the pre-mRNA (precursor-mRNA).

The pre-mRNA is processed in the nucleus to remove the introns and splice the exons together

into a translatable mRNA. That mRNA exits the nucleus and is translated in the cytoplasm.

Pre-mRNA Processing (Splicing)

Eukaryotic pre-mRNAs typically include introns. Introns are removed by RNA processing

in which the intron is looped out and cut away from the exons by snRNPs, and the exons

are spliced together to produce the translatable mRNA.
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The steps of pre-mRNA splicing (intron removal) are as follows: The intron loops out as snRNPs (small nuclear ribonucleoprotein particles, complexes of snRNAsand proteins) bind to form the spliceosome.

The intron is excised, and the exons are then spliced together.

The resulting mature mRNA may then exit the nucleus and be translated in the cytoplasm.

Transcription in ProkaryotesThe most detailed molecular information about the transcription cycle is available in

bacterial systems. The synthesis of RNA is initiated at the promoter sequence by the

enzyme RNA polymerase. A single RNA polymerase type is responsible for the

synthesis of messenger, transfer, and ribosomal RNAs.

When isolated from bacteria, prokaryotic RNA polymerase has two forms:

The coreenzyme and the holoenzyme. The core enzyme is a tetramer whose

composition is given as 2 (two alpha subunits, one beta subunit, and one beta-

prime subunit). Core RNA polymerase is capable of faithfully copying DNA into RNA

but does not initiate at the correct site in a gene. That is, it does not recognize the

promoter specifically. Correct promoter recognition is the function of the holoenzyme

form of RNA polymerase.


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Figure 1

The RNA polymerase holoenzyme contains another subunit, s( sigma), in addition to

the subunits found in the core enzyme. Holoenzyme, 2, is capable of correct

initiation at the promoter region of a gene. Sigma thus must be involved in promoter

recognition. Sigma subunits are related but distinct in different forms of RNA

polymerase holoenzyme. These specialized subunits direct RNA polymerase to

promoter sequences for different classes of genes. For example, bacteria exposed to

high temperatures synthesize a set of protective proteins called heat-shock

proteins. The genes for the heat-shock proteins have special promoter sequences

that are recognized by an RNA polymerase holoenzyme with a specific subunit.

The discussed here is the major of the common bacteriumE. coli, about which

most is known.

Promoter recognitionRNA polymerase holoenzyme starts by recognizing the promoter of a gene. The

promoter isn't copied into RNA, but it is, nonetheless, an important piece of genetic

information. The information in a promoter was determined by lining up a large

number of promoters and counting how many times a particular base appeared at a

given position in the various promoter sequences. The consensus sequence is

given by the statistically most probable base at each pointthe bases that appear

most often in the promoter collection. Very few, if any, naturally occurring

promoters match the consensus sequence exactly, but the strength of a promoter

(how actively RNA polymerase initiates at it) correlates well with the degree of

consensus match. For example, the promoters of genes for ribosomal RNA match

the consensus well, while the promoters for the mRNA encoding some regulatory

proteins match the consensus poorly. This correlates with the relative amounts of

each gene product that are needed at any one time: many ribosomes, and only a

few regulatory proteins.

The consensus sequence for an E. colipromoter has two conserved regions near

positions -35 and -10 relative to the transcription start site. That is, the template-

directed synthesis of RNA begins 35 base pairs downstream of the first consensus

region and ten base pairs downstream of the second. The -35 consensus is:

TTG ACA.

The -10 consensus is:

TATAA T.

A couple of important points exist about the consensus. First, not all bases in the

consensus are conserved to the same amount. The bases marked with bold type and

underlined are more conserved than the others, and the -10 region is more

conserved overall than is the -35 region. Secondly, the promoter sequence is

asymmetrical; that is, it reads differently in one direction than in the other.

(Compare this to the recognition sequence for the restriction enzyme BamHI,

GGATCC.) This asymmetry means that RNA polymerase gets directional


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Figure 3

Elongation is the function of the RNA polymerase core enzyme. RNA polymerase

moves along the template, locally unzipping the DNA double helix. This allows a

transient base pairing between the incoming nucleotide and newly-synthesized RNA

and the DNA template strand. As it is made, the RNA transcript forms secondary

structure through intra-strand base pairing. The average speed of transcription is

about 40 nucleotides per second, much slower than DNA polymerase. Other protein

factors may bind to polymerase and alter the rate of transcription and some specific

sequences are transcribed more slowly than others are. Eventually, RNA polymerasemust come to the end of the region to be transcribed.

Termination of transcription in vitro is classified as to its dependence on the protein

factor, rho (). Rho-independent terminators have a characteristic structure, which

features (a) A strong G-C rich stem and loop, (b) a sequence of 46 U residues in

the RNA, which are transcribed from a corresponding stretch of As in the template.

Rho-factor-dependent terminators are less well defined, as shown in Figure4.
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Ribosomal RNA

Ribosomal RNA is essential for protein synthesis. In fact, RNA is thought to be the

catalytically active part of the very large complex of proteins and RNAs that

synthesize proteins. Ribosomes and ribosomal RNAs are heterogeneous, withdifferent sized rRNAs found in the small and large subunits of the ribosome.

Ribosomes can be separated into two subunits. Each subunit contains both protein

and RNA. Although they vary widely in size, ribosomal RNAs have common

secondary structures. The larger size of the eukaryotic RNAs is due to their having

extra structural domains inserted into the midst of the smaller ones, rather than by

a totally new folding pattern.

Antibiotics are natural products, usually from soil bacteria and molds, which interfere

with the growth of other bacteria. Often these antibiotics act on ribosomal RNA

targets. For example, streptomycin, which has been used to treat tuberculosis, bindsto a single region of bacterial 16S RNA, interfering with protein synthesis. The drug

doesn't disrupt protein synthesis in humans, which allows for streptomycin's

relatively high therapeutic indexthe ratio of harmful to helpful doses of the drug.

Conversely, bacteria can become resistant to antibiotics by changes in their rRNA,

either by a change in the nucleotide sequence of the ribosomal RNA or by

methylation of the rRNA.

Transcription (genetics)From Wikipedia, the free encyclopedia


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Transcription is the process of creating acomplementaryRNAcopy of a sequence ofDNA.[1]

Both RNA

and DNA arenucleic acids, which usebase pairsofnucleotidesas acomplementarylanguage that can be

converted back and forth from DNA to RNA by the action of the correctenzymes. During transcription, a

DNA sequence is read by anRNA polymerase, which produces a complementary,antiparallelRNA strand.

As opposed toDNA replication, transcription results in an RNA complement that includesuracil(U) in all

instances wherethymine(T) would have occurred in a DNA complement. Also unlikeDNA

replicationwhere DNA is synthesised, transcription does not involve anRNA primerto initiate RNA

synthesis.

Transcription is explained easily in 4 or 5 steps, each moving like a wave along the DNA.

1. RNA polymerase moves the transcription bubble, a stretch of unpaired nucleotides, by breaking

the hydrogen bonds between complementary nucleotides.

2. RNA polymerase adds matching RNA nucleotides that are paired with complementary DNA bases.

3. RNA sugar-phosphate backbone forms with assistance from RNA polymerase.

4. Hydrogen bonds of the untwisted RNA + DNA helix break, freeing the newly synthesized RNA

strand.

5. If the cell has anucleus, the RNA is further processed (addition of a 3' poly-A tail and a 5' cap) and

exits through to the cytoplasm through thenuclear porecomplex.

Transcription is the first step leading togene expression. The stretch of DNA transcribed into an RNA

molecule is called a transcription unitand encodes at least onegene. If the gene transcribed encodes

aprotein, the result of transcription ismessenger RNA(mRNA), which will then be used to create that

protein via the process oftranslation. Alternatively, the transcribed gene may encode for eithernon-coding

RNAgenes (such asmicroRNA,lincRNA, etc.) orribosomal RNA(rRNA) ortransfer RNA(tRNA), other

components of the protein-assembly process, or otherribozymes.[2]

A DNA transcription unit encoding for a protein contains not only the sequence that will eventually be

directly translated into the protein (the coding sequence) but also regulatory sequencesthat direct and

regulate the synthesis of that protein. The regulatory sequence before (upstreamfrom) the coding

sequence is called thefive prime untranslated region(5'UTR), and the sequence following

(downstreamfrom) the coding sequence is called thethree prime untranslated region(3'UTR).[2]

Transcription has some proofreading mechanisms, but they are fewer and less effective than the controls

for copying DNA; therefore, transcription has a lower copying fidelity than DNA replication .[3]

As in DNA replication, DNA is read from 3' 5' during transcription. Meanwhile, the complementary RNA

is created from the 5' 3' direction. This means its 5' end is created first in base pairing. Although DNA is

arranged as two antiparallel strands in adouble helix, only one of the two DNA strands, called the template

strand, is used for transcription. This is because RNA is only single-stranded, as opposed to double-

stranded DNA. The other DNA strand is called the coding (lagging) strand, because its sequence is the
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n.wikipedia.org/wiki/Transcription_(genetics)#cite_note-Stryer_2006-2http://en.wikipedia.org/wiki/Double_helixhttp://en.wikipedia.org/wiki/Double_helixhttp://en.wikipedia.org/wiki/Double_helixhttp://en.wikipedia.org/wiki/Double_helixhttp://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-Stryer_2006-2http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-Biology-1http://en.wikipedia.org/wiki/Three_prime_untranslated_regionhttp://en.wikipedia.org/wiki/Upstream_and_downstream_(DNA)http://en.wikipedia.org/wiki/Five_prime_untranslated_regionhttp://en.wikipedia.org/wiki/Upstream_and_downstream_(DNA)http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-Biology-1http://en.wikipedia.org/wiki/Ribozymehttp://en.wikipedia.org/wiki/Transfer_RNAhttp://en.wikipedia.org/wiki/Ribosomal_RNAhttp://en.wikipedia.org/wiki/LincRNAhttp://en.wikipedia.org/wiki/MicroRNAhttp://en.wikipedia.org/wiki/Non-coding_RNAhttp://en.wikipedia.org/wiki/Non-coding_RNAhttp://en.wikipedia.org/wiki/Translation_(genetics)http://en.wikipedia.org/wiki/Messenger_RNAhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/Gene_expressionhttp://en.wikipedia.org/wiki/Nuclear_porehttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Primer_(molecular_biology)http://en.wikipedia.org/wiki/DNA_replicationhttp://en.wikipedia.org/wiki/DNA_replicationhttp://en.wikipedia.org/wiki/Thyminehttp://en.wikipedia.org/wiki/Uracilhttp://en.wikipedia.org/wiki/DNA_replicationhttp://en.wikipedia.org/wiki/Antiparallel_(biochemistry)http://en.wikipedia.org/wiki/RNA_polymerasehttp://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Complementarity_(molecular_biology)http://en.wikipedia.org/wiki/Nucleotidehttp://en.wikipedia.org/wiki/Base_pairhttp://en.wikipedia.org/wiki/Nucleic_acidhttp://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-0http://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/Complementarity_(molecular_biology)


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same as the newly created RNA transcript (except for the substitution of uracil for thymine). The use of only

the 3' 5' strand eliminates the need for theOkazaki fragmentsseen in DNA replication.[2]

Transcription is divided into 5 stages: pre-initiation, initiation, promoter

clearance, elongationand termination.

[2]

Contents

[hide]

1 Major steps

o 1.1 Pre-initiation

o 1.2 Initiation

o 1.3 Promoter clearance

o 1.4 Elongation

o 1.5 Termination

2 Measuring and detecting transcription

3 Transcription factories

4 History

5 Reverse transcription

6 Inhibitors

7 See also

8 References

9 External links

[edit]Major steps

[edit]Pre-initiation

In eukaryotes,RNA polymerase, and therefore the initiation of transcription, requires the presence of a

corepromotersequence in the DNA. Promoters are regions of DNA that promote transcription and, in

eukaryotes, are found at -30, -75, and -90 base pairs upstream from the transcription start site(abbreviated

to TSS). Core promoters are sequences within the promoter that are essential for transcription initiation.

RNA polymerase is able to bind to core promoters in the presence of various specific transcription

factors.[citation needed]

The most characterized type of core promoter in eukaryotes is a short DNA sequence known as aTATA

box, found 25-30 base pairs upstream from the TSS.[citation needed]

The TATA box, as a core promoter, is the

binding site for a transcription factor known asTATA-binding protein(TBP), which is itself a subunit of

another transcription factor, calledTranscription Factor II D(TFIID). After TFIID binds to the TATA box via

the TBP, five more transcription factors and RNA polymerase combine around the TATA box in a series of

stages to form apreinitiation complex. One transcription factor,Transcription factor II H, has two
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ttp://en.wikipedia.org/wiki/Transcription_preinitiation_complexhttp://en.wikipedia.org/wiki/Transcription_Factor_II_Dhttp://en.wikipedia.org/wiki/TATA-binding_proteinhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/TATA_boxhttp://en.wikipedia.org/wiki/TATA_boxhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Transcription_factorhttp://en.wikipedia.org/wiki/Transcription_factorhttp://en.wikipedia.org/wiki/Transcription_start_sitehttp://en.wikipedia.org/wiki/Promoter_(biology)http://en.wikipedia.org/wiki/RNA_polymerasehttp://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=2http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=1http://en.wikipedia.org/wiki/Transcription_(genetics)#External_linkshttp://en.wikipedia.org/wiki/Transcription_(genetics)#Referenceshttp://en.wikipedia.org/wiki/Transcription_(genetics)#See_alsohttp://en.wikipedia.org/wiki/Transcription_(genetics)#Inhibitorshttp://en.wikipedia.org/wiki/Transcription_(genetics)#Reverse_transcriptionhttp://en.wikipedia.org/wiki/Transcription_(genetics)#Historyhttp://en.wikipedia.org/wiki/Transcription_(genetics)#Transcription_factorieshttp://en.wikipedia.org/wiki/Transcription_(genetics)#Measuring_and_detecting_transcriptionhttp://en.wikipedia.org/wiki/Transcription_(genetics)#Terminationhttp://en.wikipedia.org/wiki/Transcription_(genetics)#Elongationhttp://en.wikipedia.org/wiki/Transcription_(genetics)#Promoter_clearancehttp://en.wikipedia.org/wiki/Transcription_(genetics)#Initiationhttp://en.wikipedia.org/wiki/Transcription_(genetics)#Pre-initiationhttp://en.wikipedia.org/wiki/Transcription_(genetics)#Major_stepshttp://en.wikipedia.org/wiki/Transcription_(genetics)http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-Biology-1http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-Biology-1http://en.wikipedia.org/wiki/Okazaki_fragment


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components withhelicaseactivity and so is involved in the separating of opposing strands of double-

stranded DNA to form the initial transcription bubble. However, only a low, or basal, rate of transcription is

driven by the preinitiation complex alone. Other proteins known asactivatorsandrepressors, along with

any associatedcoactivatorsorcorepressors, are responsible for modulating transcription rate.[citation needed]

Thus, preinitiation complex contains:[citation needed]

1. Core Promoter Sequence 2. Transcription Factors 3.

RNA Polymerase 4. Activators and Repressors. The transcription preinitiation inarchaeais, in essence,

homologous to that of eukaryotes, but is much less complex.[4]

The archaeal preinitiation complex

assembles at a TATA-box binding site; however, in archaea, this complex is composed of only RNA

polymerase II, TBP, and TFB (the archaeal homologue of eukaryotictranscription factor II B(TFIIB)).[5][6]

[edit]Initiation

Simple diagram of transcription initiation. RNAP = RNA polymerase

Inbacteria, transcription begins with the binding of RNA polymerase to the promoter in DNA. RNA

polymerase is acore enzymeconsisting of five subunits: 2 subunits, 1 subunit, 1 ' subunit, and 1

subunit. At the start of initiation, the core enzyme is associated with asigma factorthat aids in finding the

appropriate -35 and -10 base pairs downstream ofpromotersequences.[7]

When the sigma factor and RNA

polymerase combine, they form a holoenzyme.

Transcription initiation is more complex in eukaryotes. Eukaryotic RNA polymerase does not directly

recognize the core promoter sequences. Instead, a collection of proteins calledtranscription

factorsmediate the binding of RNA polymerase and the initiation of transcription. Only after certain

transcription factors are attached to the promoter does the RNA polymerase bind to it. The completed

assembly of transcription factors and RNA polymerase bind to the promoter, forming a transcription

initiation complex. Transcription in the archaea domain is similar to transcription in eukaryotes.[8]

[edit]Promoter clearance

After the first bond is synthesized, the RNA polymerase must clear the promoter. During this time there is a

tendency to release the RNA transcript and produce truncated transcripts. This is called abortive

initiationand is common for both eukaryotes and prokaryotes.[9]

Abortive initiation continues to occur until

the factor rearranges, resulting in the transcription elongation complex (which gives a 35 bp moving

footprint). The factor is released before 80 nucleotides of mRNA are synthesized .[10]

Once the transcript

reaches approximately 23 nucleotides, it no longer slips and elongation can occur. This, like most of the
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remainder of transcription, is anenergy-dependent process, consumingadenosine

triphosphate(ATP).[citation needed]

Promoter clearance coincides with phosphorylation of serine 5 on the carboxy terminal domain of RNAP II

in eukaryotes, which is phosphorylated by TFIIH.

[citation needed]

[edit]Elongation

Simple diagram of transcription elongation

One strand of the DNA, the template strand(or noncoding strand), is used as a template for RNA

synthesis. As transcription proceeds, RNA polymerase traverses the template strand and uses base pairing

complementarity with the DNA template to create an RNA copy. Although RNA polymerase traverses the

template strand from 3' 5', the coding (non-template) strand and newly-formed RNA can also be used as

reference points, so transcription can be described as occurring 5' 3'. This produces an RNA molecule

from 5' 3', an exact copy of the coding strand (except thatthyminesare replaced withuracils, and the

nucleotides are composed of a ribose (5-carbon) sugar where DNA has deoxyribose (one less oxygen

atom) in its sugar-phosphate backbone).[citation needed]

Unlike DNA replication, mRNA transcription can involve multiple RNA polymerases on a single DNA

template and multiple rounds of transcription (amplification of particular mRNA), so many mRNA molecules

can be rapidly produced from a single copy of a gene.[citation needed]

Elongation also involves a proofreading mechanism that can replace incorrectly incorporated bases. In

eukaryotes, this may correspond with short pauses during transcription that allow appropriate RNA editing

factors to bind. These pauses may be intrinsic to the RNA polymerase or due to chromatin structure.[citation

needed]

[edit]Termination

Bacteria use two different strategies for transcription termination.1.Rho-independent transcription 2.Rho-

dependent transcription. InRho-independent transcription termination,also called intrinsic termination, RNA

transcription stops when the newly synthesized RNA molecule forms a G-C-richhairpin loopfollowed by a

run of Us. When the hairpin forms, the mechanical stress breaks the weak rU-dA bonds, now filling the

DNA-RNA hybrid. This pulls the poly-U transcript out of the active site of the RNA polymerase, in effect,

terminating transcription. In the "Rho-dependent" type of termination, a protein factor called "Rho"

destabilizes the interaction between the template and the mRNA, thus releasing the newly synthesized

mRNA from the elongation complex.[11]
http://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=5http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=5http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=5http://en.wikipedia.org/wiki/Thyminehttp://en.wikipedia.org/wiki/Thyminehttp://en.wikipedia.org/wiki/Thyminehttp://en.wikipedia.org/wiki/Uracilhttp://en.wikipedia.org/wiki/Uracilhttp://en.wikipedia.org/wiki/Uracilhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=6http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=6http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=6http://en.wikipedia.org/wiki/Rho-independent_transcription_terminationhttp://en.wikipedia.org/wiki/Rho-independent_transcription_terminationhttp://en.wikipedia.org/wiki/Rho-independent_transcription_terminationhttp://en.wikipedia.org/wiki/Hairpin_loophttp://en.wikipedia.org/wiki/Hairpin_loophttp://en.wikipedia.org/wiki/Hairpin_loophttp://en.wikipedia.org/wiki/Rho_factorhttp://en.wikipedia.org/wiki/Rho_factorhttp://en.wikipedia.org/wiki/Rho_factorhttp://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-10http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-10http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-10http://en.wikipedia.org/wiki/File:Simple_transcription_elongation1.svghttp://en.wikipedia.org/w/index.php?title=File:Simple_transcription_elongation1.svg&page=1http://en.wikipedia.org/wiki/File:Simple_transcription_elongation1.svghttp://en.wikipedia.org/w/index.php?title=File:Simple_transcription_elongation1.svg&page=1http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-10http://en.wikipedia.org/wiki/Rho_factorhttp://en.wikipedia.org/wiki/Hairpin_loophttp://en.wikipedia.org/wiki/Rho-independent_transcription_terminationhttp://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=6http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Uracilhttp://en.wikipedia.org/wiki/Thyminehttp://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=5http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Energy


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Transcription termination in eukaryotes is less understood but involves cleavage of the new transcript

followed by template-independent addition ofAs at its new 3' end, in a process calledpolyadenylation.[12]

[edit]Measuring and detecting transcription

Electron micrographof the ribosomal transcription process. The formingmRNAstrands are visible as branches from the

main DNA strand.[citation needed]

Transcription can be measured and detected in a variety of ways:[citation needed]

Nuclear Run-on assay: measures the relative abundance of newly formed transcripts

RNase protection assayandChIP-ChipofRNAP: detect active transcription sites

RT-PCR: measures the absolute abundance of total or nuclear RNA levels, which may however differ

from transcription rates

DNA microarrays: measures the relative abundance of the global total or nuclear RNA levels; however,

these may differ from transcription rates

In situ hybridization: detects the presence of a transcript

MS2 tagging: by incorporating RNAstem loops, such as MS2, into a gene, these become incorporated

into newly synthesized RNA. The stem loops can then be detected using a fusion of GFP and the MS2

coat protein, which has a high affinity, sequence-specific interaction with the MS2 stem loops. The

recruitment of GFP to the site of transcription is visualised as a single fluorescent spot. This

remarkable new approach has revealed that transcription occurs in discontinuous bursts, or pulses

(seeTranscriptional bursting). With the notable exception of in situ techniques, most other methods

provide cell population averages, and are not capable of detecting this fundamental property of

genes.[13]

Northern blot: the traditional method, and until the advent ofRNA-Seq, the most quantitative
http://en.wikipedia.org/wiki/Polyadenylationhttp://en.wikipedia.org/wiki/Polyadenylationhttp://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-11http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-11http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-11http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=7http://en.wikipedia.org/wiki/Electron_micrographhttp://en.wikipedia.org/wiki/Electron_micrographhttp://en.wikipedia.org/wiki/MRNAhttp://en.wikipedia.org/wiki/MRNAhttp://en.wikipedia.org/wiki/MRNAhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Nuclear_run-onhttp://en.wikipedia.org/wiki/Nuclear_run-onhttp://en.wikipedia.org/wiki/RNase_protection_assayhttp://en.wikipedia.org/wiki/RNase_protection_assayhttp://en.wikipedia.org/wiki/ChIP-Chiphttp://en.wikipedia.org/wiki/ChIP-Chiphttp://en.wikipedia.org/wiki/ChIP-Chiphttp://en.wikipedia.org/wiki/RNAPhttp://en.wikipedia.org/wiki/RNAPhttp://en.wikipedia.org/wiki/RNAPhttp://en.wikipedia.org/wiki/RT-PCRhttp://en.wikipedia.org/wiki/RT-PCRhttp://en.wikipedia.org/wiki/DNA_microarrayshttp://en.wikipedia.org/wiki/DNA_microarrayshttp://en.wikipedia.org/wiki/In_situ_hybridizationhttp://en.wikipedia.org/wiki/In_situ_hybridizationhttp://en.wikipedia.org/wiki/MS2_tagginghttp://en.wikipedia.org/wiki/MS2_tagginghttp://en.wikipedia.org/wiki/Stem-loophttp://en.wikipedia.org/wiki/Stem-loophttp://en.wikipedia.org/wiki/Stem-loophttp://en.wikipedia.org/wiki/Transcriptional_burstinghttp://en.wikipedia.org/wiki/Transcriptional_burstinghttp://en.wikipedia.org/wiki/Transcriptional_burstinghttp://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-12http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-12http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-12http://en.wikipedia.org/wiki/Northern_blothttp://en.wikipedia.org/wiki/Northern_blothttp://en.wikipedia.org/wiki/RNA-Seqhttp://en.wikipedia.org/wiki/RNA-Seqhttp://en.wikipedia.org/wiki/RNA-Seqhttp://en.wikipedia.org/wiki/File:Transcription_label_en.jpghttp://en.wikipedia.org/wiki/File:Transcription_label_en.jpghttp://en.wikipedia.org/wiki/File:Transcription_label_en.jpghttp://en.wikipedia.org/wiki/File:Transcription_label_en.jpghttp://en.wikipedia.org/wiki/RNA-Seqhttp://en.wikipedia.org/wiki/Northern_blothttp://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-12http://en.wikipedia.org/wiki/Transcriptional_burstinghttp://en.wikipedia.org/wiki/Stem-loophttp://en.wikipedia.org/wiki/MS2_tagginghttp://en.wikipedia.org/wiki/In_situ_hybridizationhttp://en.wikipedia.org/wiki/DNA_microarrayshttp://en.wikipedia.org/wiki/RT-PCRhttp://en.wikipedia.org/wiki/RNAPhttp://en.wikipedia.org/wiki/ChIP-Chiphttp://en.wikipedia.org/wiki/RNase_protection_assayhttp://en.wikipedia.org/wiki/Nuclear_run-onhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/MRNAhttp://en.wikipedia.org/wiki/Electron_micrographhttp://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=7http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-11http://en.wikipedia.org/wiki/Polyadenylation


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RNA-Seq: applies next-generation sequencing techniques to sequence whole transcriptomes, which

allows the measurement of relative abundance of RNA, as well as the detection of additional variations

such as fusion genes, post-translational edits and novel splice sites

[edit]Transcription factories

Main article:Transcription factories

Active transcription units are clustered in the nucleus, in discrete sites calledtranscription

factoriesoreuchromatin. Such sites can be visualized by allowing engaged polymerases to extend their

transcripts in tagged precursors (Br-UTP or Br-U) and immuno-labeling the tagged nascent RNA.

Transcription factories can also be localized using fluorescence in situ hybridization or marked by

antibodies directed against polymerases. There are ~10,000 factories in the nucleoplasm of a HeLa cell,

among which are ~8,000 polymerase II factories and ~2,000 polymerase III factories. Each polymerase II

factory contains ~8 polymerases. As most active transcription units are associated with only one

polymerase, each factory usually contains ~8 different transcription units. These units might be associated

through promoters and/or enhancers, with loops forming a cloud around the factor.[citation needed]

[edit]History

A molecule that allows the genetic material to be realized as a protein was first hypothesized byFranois

JacobandJacques Monod.Severo Ochoawon aNobel Prize in Physiology or Medicinefor developing a

process of RNA synthesis in 1959. RNA synthesis by RNA polymerase was established in vitroby several

laboratories by 1965; however, the RNA synthesized by these enzymes had properties that suggested the

existence of an additional factor needed to terminate transcription correctly.[citation needed]

In 1972, Walter Fiers became the first person to actually prove the existence of the terminating enzyme.

Roger D. Kornbergwon the 2006Nobel Prize in Chemistry"for his studies of the molecular basis of

eukaryotic transcription".[14]

[edit]Reverse transcription
http://en.wikipedia.org/wiki/RNA-Seqhttp://en.wikipedia.org/wiki/RNA-Seqhttp://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=8http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=8http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=8http://en.wikipedia.org/wiki/Transcription_factorieshttp://en.wikipedia.org/wiki/Transcription_factorieshttp://en.wikipedia.org/wiki/Transcription_factorieshttp://en.wikipedia.org/wiki/Transcription_factorieshttp://en.wikipedia.org/wiki/Transcription_factorieshttp://en.wikipedia.org/wiki/Transcription_factorieshttp://en.wikipedia.org/wiki/Transcription_factorieshttp://en.wikipedia.org/wiki/Euchromatinhttp://en.wikipedia.org/wiki/Euchromatinhttp://en.wikipedia.org/wiki/Euchromatinhttp://en.wikipedia.org/wiki/HeLa_cellhttp://en.wikipedia.org/wiki/HeLa_cellhttp://en.wikipedia.org/wiki/HeLa_cellhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=9http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=9http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=9http://en.wikipedia.org/wiki/Fran%C3%A7ois_Jacobhttp://en.wikipedia.org/wiki/Fran%C3%A7ois_Jacobhttp://en.wikipedia.org/wiki/Fran%C3%A7ois_Jacobhttp://en.wikipedia.org/wiki/Fran%C3%A7ois_Jacobhttp://en.wikipedia.org/wiki/Jacques_Monodhttp://en.wikipedia.org/wiki/Jacques_Monodhttp://en.wikipedia.org/wiki/Jacques_Monodhttp://en.wikipedia.org/wiki/Severo_Ochoahttp://en.wikipedia.org/wiki/Severo_Ochoahttp://en.wikipedia.org/wiki/Severo_Ochoahttp://en.wikipedia.org/wiki/Nobel_Prize_in_Physiology_or_Medicinehttp://en.wikipedia.org/wiki/Nobel_Prize_in_Physiology_or_Medicinehttp://en.wikipedia.org/wiki/Nobel_Prize_in_Physiology_or_Medicinehttp://en.wikipedia.org/wiki/In_vitrohttp://en.wikipedia.org/wiki/In_vitrohttp://en.wikipedia.org/wiki/In_vitrohttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Roger_D._Kornberghttp://en.wikipedia.org/wiki/Roger_D._Kornberghttp://en.wikipedia.org/wiki/Nobel_Prize_in_Chemistryhttp://en.wikipedia.org/wiki/Nobel_Prize_in_Chemistryhttp://en.wikipedia.org/wiki/Nobel_Prize_in_Chemistryhttp://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-13http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-13http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-13http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=10http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=10http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=10http://en.wikipedia.org/wiki/File:RetroTranscription.jpghttp://en.wikipedia.org/wiki/File:RetroTranscription.jpghttp://en.wikipedia.org/wiki/File:RetroTranscription.jpghttp://en.wikipedia.org/wiki/File:RetroTranscription.jpghttp://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=10http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-13http://en.wikipedia.org/wiki/Nobel_Prize_in_Chemistryhttp://en.wikipedia.org/wiki/Roger_D._Kornberghttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/In_vitrohttp://en.wikipedia.org/wiki/Nobel_Prize_in_Physiology_or_Medicinehttp://en.wikipedia.org/wiki/Severo_Ochoahttp://en.wikipedia.org/wiki/Jacques_Monodhttp://en.wikipedia.org/wiki/Fran%C3%A7ois_Jacobhttp://en.wikipedia.org/wiki/Fran%C3%A7ois_Jacobhttp://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=9http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/HeLa_cellhttp://en.wikipedia.org/wiki/Euchromatinhttp://en.wikipedia.org/wiki/Transcription_factorieshttp://en.wikipedia.org/wiki/Transcription_factorieshttp://en.wikipedia.org/wiki/Transcription_factorieshttp://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=8http://en.wikipedia.org/wiki/RNA-Seq


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Scheme of reverse transcription

Someviruses(such asHIV, the cause ofAIDS), have the ability to transcribe RNA into DNA. HIV has an

RNA genome that is duplicated into DNA. The resulting DNA can be merged with the DNA genome of the

host cell. The main enzyme responsible for synthesis of DNA from an RNA template is called reverse

transcriptase. In the case of HIV, reverse transcriptase is responsible for synthesizing a complementary

DNAstrand (cDNA) to the viral RNA genome. An associated enzyme, ribonuclease H, digests the RNA

strand, and reverse transcriptase synthesises a complementary strand of DNA to form a double helix DNA

structure. This cDNA is integrated into the host cell's genome via another enzyme (integrase) causing the

host cell to generate viral proteins that reassemble into new viral particles. In HIV, subsequent to this, the

host cell undergoes programmed cell death,apoptosisofT cells.[15]

However, in other retroviruses, the host

cell remains intact as the virus buds out of the cell.

Some eukaryotic cells contain an enzyme with reverse transcription activity called telomerase. Telomerase

is a reverse transcriptase that lengthens the ends of linear chromosomes. Telomerase carries an RNA

template from which it synthesizes DNA repeating sequence, or "junk" DNA. This repeated sequence of

DNA is important because, every time a linear chromosome is duplicated, it is shortened in length. With

"junk" DNA at the ends of chromosomes, the shortening eliminates some of the non-essential, repeated

sequence rather than the protein-encoding DNA sequence farther away from the chromosome end.

Telomerase is often activated in cancer cells to enable cancer cells to duplicate their genomes indefinitely

without losing important protein-coding DNA sequence. Activation of telomerase could be part of the

process that allows cancer cells to become immortal. However, the truein vivosignificance of telomerasehas still not beenempiricallyproven.

[citation needed]

[edit]Inhibitors

Transcription inhibitors can be used asantibioticsagainst, for example,pathogenic bacteria(antibacterials)

andfungi(antifungals). An example of such an antibacterial isrifampicin, which inhibitsprokaryotic DNA

transcriptioninto mRNA by inhibiting DNA-dependentRNA polymeraseby binding its beta-subunit.8-

Hydroxyquinolineis an antifungal transcription inhibitor.[16]

[edit]

See also
http://en.wikipedia.org/wiki/Viruseshttp://en.wikipedia.org/wiki/Viruseshttp://en.wikipedia.org/wiki/Viruseshttp://en.wikipedia.org/wiki/HIVhttp://en.wikipedia.org/wiki/HIVhttp://en.wikipedia.org/wiki/HIVhttp://en.wikipedia.org/wiki/AIDShttp://en.wikipedia.org/wiki/AIDShttp://en.wikipedia.org/wiki/AIDShttp://en.wikipedia.org/wiki/Reverse_transcriptasehttp://en.wikipedia.org/wiki/Reverse_transcriptasehttp://en.wikipedia.org/wiki/Reverse_transcriptasehttp://en.wikipedia.org/wiki/Reverse_transcriptasehttp://en.wikipedia.org/wiki/Complementary_DNAhttp://en.wikipedia.org/wiki/Complementary_DNAhttp://en.wikipedia.org/wiki/Complementary_DNAhttp://en.wikipedia.org/wiki/Integrasehttp://en.wikipedia.org/wiki/Integrasehttp://en.wikipedia.org/wiki/Integrasehttp://en.wikipedia.org/wiki/Apoptosishttp://en.wikipedia.org/wiki/Apoptosishttp://en.wikipedia.org/wiki/Apoptosishttp://en.wikipedia.org/wiki/T_cellhttp://en.wikipedia.org/wiki/T_cellhttp://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-14http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-14http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-14http://en.wikipedia.org/wiki/Telomerasehttp://en.wikipedia.org/wiki/Telomerasehttp://en.wikipedia.org/wiki/Telomerasehttp://en.wikipedia.org/wiki/In_vivohttp://en.wikipedia.org/wiki/In_vivohttp://en.wikipedia.org/wiki/In_vivohttp://en.wikipedia.org/wiki/Empiricalhttp://en.wikipedia.org/wiki/Empiricalhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=11http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=11http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=11http://en.wikipedia.org/wiki/Antibiotichttp://en.wikipedia.org/wiki/Antibiotichttp://en.wikipedia.org/wiki/Antibiotichttp://en.wikipedia.org/wiki/Pathogenic_bacteriahttp://en.wikipedia.org/wiki/Pathogenic_bacteriahttp://en.wikipedia.org/wiki/Pathogenic_bacteriahttp://en.wikipedia.org/wiki/Antibacterialhttp://en.wikipedia.org/wiki/Antibacterialhttp://en.wikipedia.org/wiki/Antibacterialhttp://en.wikipedia.org/wiki/Fungushttp://en.wikipedia.org/wiki/Fungushttp://en.wikipedia.org/wiki/Fungushttp://en.wikipedia.org/wiki/Antifungal_medicationhttp://en.wikipedia.org/wiki/Antifungal_medicationhttp://en.wikipedia.org/wiki/Antifungal_medicationhttp://en.wikipedia.org/wiki/Rifampicinhttp://en.wikipedia.org/wiki/Rifampicinhttp://en.wikipedia.org/wiki/Rifampicinhttp://en.wikipedia.org/wiki/Prokaryotic_transcriptionhttp://en.wikipedia.org/wiki/Prokaryotic_transcriptionhttp://en.wikipedia.org/wiki/Prokaryotic_transcriptionhttp://en.wikipedia.org/wiki/RNA_polymerasehttp://en.wikipedia.org/wiki/RNA_polymerasehttp://en.wikipedia.org/wiki/RNA_polymerasehttp://en.wikipedia.org/wiki/8-Hydroxyquinolinehttp://en.wikipedia.org/wiki/8-Hydroxyquinolinehttp://en.wikipedia.org/wiki/8-Hydroxyquinolinehttp://en.wikipedia.org/wiki/8-Hydroxyquinolinehttp://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-15http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-15http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-15http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=12http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=12http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=12http://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=12http://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-15http://en.wikipedia.org/wiki/8-Hydroxyquinolinehttp://en.wikipedia.org/wiki/8-Hydroxyquinolinehttp://en.wikipedia.org/wiki/RNA_polymerasehttp://en.wikipedia.org/wiki/Prokaryotic_transcriptionhttp://en.wikipedia.org/wiki/Prokaryotic_transcriptionhttp://en.wikipedia.org/wiki/Rifampicinhttp://en.wikipedia.org/wiki/Antifungal_medicationhttp://en.wikipedia.org/wiki/Fungushttp://en.wikipedia.org/wiki/Antibacterialhttp://en.wikipedia.org/wiki/Pathogenic_bacteriahttp://en.wikipedia.org/wiki/Antibiotichttp://en.wikipedia.org/w/index.php?title=Transcription_(genetics)&action=edit&section=11http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Empiricalhttp://en.wikipedia.org/wiki/In_vivohttp://en.wikipedia.org/wiki/Telomerasehttp://en.wikipedia.org/wiki/Transcription_(genetics)#cite_note-14http://en.wikipedia.org/wiki/T_cellhttp://en.wikipedia.org/wiki/Apoptosishttp://en.wikipedia.org/wiki/Integrasehttp://en.wikipedia.org/wiki/Complementary_DNAhttp://en.wikipedia.org/wiki/Complementary_DNAhttp://en.wikipedia.org/wiki/Reverse_transcriptasehttp://en.wikipedia.org/wiki/Reverse_transcriptasehttp://en.wikipedia.org/wiki/AIDShttp://en.wikipedia.org/wiki/HIVhttp://en.wikipedia.org/wiki/Viruses

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