tarnscription rna polymerase

8/14/2019 tarnscription RNA POLYMERASE

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By Alberts


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TBP

TATA

By Alberts


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By Alberts


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Mechanisms of transcription by Pol II


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Structure of RNAPII and interaction of the enzyme with promoter DNA. This schematic representationof the polymerase (shown in orange) emphasizes the way in which the clamp and wall domains restrict accessto the active site. Subunits Rpb4 and Rpb7 form a complex (shown in blue) that can dissociate from the coreenzyme, and might play a role in helping to determine the position of the clamp domain. The Rpb4Rpb7 complexmay also be involved in interaction with newly synthesized RNA. The narrow configuration of the active site cleftprobably requires melting of the transcription start region for the template strand to reach the RNAPII active site(indicated by the red dot).

Asturias FJ. 2004. Curr Opin Struct Biol . 14(2):121-9. Review.


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RNA polymerase II transcription initiation complex. X-ray and electron microscopestructures (upper left) were assembled in a complete transcription initiation complex(lower right).

By Kornberg, (2005) FEBS Letters, 579, 899-903


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Action of Mediator


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The yeast RNA Polymerase II holoenzyme revealed by electron microscopy and image processing.(A) The extended Mediator contains three distinguishable regions; head (h), middle (m),and tail (t). The globular density embraced by Mediator is identified as RNA polymerase II. The outline of a

projection of the previously determined polymerase three-dimensional structure is superimposed (dark line),with the point of attachment of the C-terminal domain (dark circle) and the location of the DNA-binding channel(c) indicated. (B) Tentative subunit organization for the holoenzyme. The model is based on available structuralInformation and reported physical interactions. The surface of each subunit has been calculated by assuminga globular shape and drawn in scale. Subunits in red have reported homologs in Saccharomyces pombe and,with the exception of Rox3 and Srb6, also in mammalian Mediator. The yellow subunits are specific for Saccharomyces cerevisiae .

Tail

By Bjorklund & Gustafsson, (2004) Advance in Protein Chem., 67, 43-65


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Mediator and its interaction with the basal transcription machinery. The structure of the RNAPIIMediator complex has revealed the way in which RNAPII interacts with the Mediator complex. As shown, upstream promoter DNA, IIB and TBP are all expected to be located at the interface between polymerase and Mediator. This implies thatRNAPII and Mediator cannot arrive at a promoter as a pre-formed complex, but must be recruited independently.

Asturias FJ. 2004. Curr Opin Struct Biol . 14(2):121-9. Review.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Display&dopt=pubmed_pubmed&from_uid=15093825http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Display&dopt=pubmed_pubmed&from_uid=15093825


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Model Depicting the Sequential Steps Involved in the Formation of an Active Pre-initiationComplex on the HNF-4 Regulatory Region.

1. Poised or committed state of the HNF-4 gene

2. Recruitment of CBP, P/CAF, and Brg-1 to theenhancer region and assembly of the RNA pol-IIholoenzyme at the proximal promoter region.

3. Unidirectional movement of the DNA-proteincomplex formed on the HNF-4 enhancer alongthe intervening sequences and spreading of histone hyperacetylation.

4. Formation of a stable enhancer-promoter complex, hyperacetylation of nucleosomeslocated at the promoter, remodeling of thenucleosome located at the transcriptionstart site, and release of RNA pol-II from thepromoter.

Hatzis P, Talianidis I. 2002. Mol Cell 10(6):1467-77.


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What is transcription?Transcription is a process that cell selectively copies a particularportion of its genetic information from DNA - a gene - to RNA.

TRANSCRIPTION TRANSCRIPTION

Gene A Gene B

Transcription is a process of DNA template-directed RNApolymerization, or an ordered linkage of ATP, CTP, UTP and GTPthrough phosphodiester bonds in 5 to 3 direction, with the nucleotideorder determined by complementary base pairing.


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Features:It uses one DNA strand as a template.It does not need primers.It synthesizes RNA from 5 to 3(unidirectional).DNA duplex unwinds upstream and rewinds downstream of the transcription bubble.It involves the function of multiple enzymes and proteins.


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Types of RNA FunctionmRNAs code for proteinsrRNAs form the structure of ribosomes and catalyze protein synthesistRNAs functions as adaptors between mRNAs and amino acidssnRNAs functions in processes such as pre-mRNA splicing

Lectures are focused on RNA polymerase II (Pol II)-mediatedtranscription.

Polymerase Product Regulation Stability Site of synthesisI rRNA simple high nucleolus

II precursor of mRNA very diverse low nucleoplasm

III tRNA, small RNA simple high nucleoplasm

Three principal types of RNA polymerases in humancells synthesize RNAs with different functions


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The three stages of transcription:Initiation, elongation and termination.

Signals that control RNA polymerases where to startand stop are encoded in DNA.

TRANSCRIPTIONTRANSCRIPTION

Gene AGene B

Initiation is the main point at which cells regulate transcription.


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InitiationThe selection of a DNA segment to be transcribed is made by theformation of an initiation complex at the promoter .Promoter: a short region of DNA sequences that specifies the

association of RNA polymerase complex to initiate transcription.

5TATTGACATATAATStart site

-35 -10 +1The sigma factor in E. coli interacts with the 35 and 10sequences at the promoters to select genes for the RNApolymerase to transcribe.

Consensus sequences of E. coli promoter


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tarnscription rna polymerase

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