Mobile DNA sequencesCause mutations in adjacent genesCause chromosomal rearrangementsRelocate genes

The RNA virusConvert its sequence into DNA by Reverse transcriptaseInfectiousPROVIRUS:A duplex DNA seq.Integrated into eukaryoticgenomeRepresent RNA seq. of RetrovirusRETROTRANSPOSONS:generate nucleoprotein capsids but no mature virus particles are formedDo not undergo an extracellular phase

Flanking direct repeats( 3 t0 12bp)Terminal inverted repeats(9 to 40bp)Transposase enzyme

Resolvase enzymeSpecial genes:

Antibiotic resistanceEX. KANR ,TETR

R RU5 U3

CLASS 1: DNA TYPE ELEMENTS CLASS 2: RETROELEMENTS

TRANSPOSITION BY: DNA INTERMEDIATE TRANSPOSE WITHIN GENOME

TRANSPOSITION BY: RNA INTERMEDIATETRANSPOSE BETWEEN GENOMES

MAY CAUSE MUTATION MAY COUSE INFECTION

MAY OR MAY NOT SHOW PHENOTYPIC CHANGE

MAY ALTER THE PROPERTIES OF THE INFECTED CELL

CELLULAR SEQUENCES CAN RECOMBINE WITH TE BUT CAN NOT BE TRANSDUSED

CELLULAR SEQUENCES RECOMBINE WITH RETROVIRAL SEQUENCES AND TRANSDUSED

PRESENT IN BOTH PROKARYOTES AND EUKARYOTES

PRESENT ONLY IN EUKARYOTES

GENES ENCODED: TRANSPOSASE , RESOLVASE AND SOMETIMES SPECIAL GENES

GENES ENCODE: REVERSE TRANSCRIPTASE, INTEGRASE

CLASS 1: DNA TYPE ELEMENTS CLASS 2: RETROELEMENTS

BACTERIAL TRANSPOSONS

EUKARYOTICTRANSPOSONS

RETROTRANSPOSONS RETROPOSONS

ABUNDANTCARRY GENES REQUIRED FOR ITS OWN TRANSPOSITIONGENERAL ORGENIZATION: TERMINAL INVERTED REPETS, FLANKING DIRECT REPETES, TRANSPOSASE GENE

NOT WELLCHARACTERIZEDBUT CAMPARABLE SYSTEMS ARE PRESENTGENERAL ORGANIZATION:TERMINAL INVERTED REPETS, FLANKING DIRECT REPETES, TRANSPOSASE GENE

LTR TRANSPOSONSCLOSELY RELETED TO RETROVIRUSESSOURCE OF MOBILITY:DNARNADNATERMINAL REPEATS:4-6bpMAY CAONTAINS INTRONS( REMOVED IN SUBGENOMIC mRNA)

NON-LTR TRANSPOSONSSOURCE OF MOBILITY:RNA INTERMEDIATETERMINAL REPEATS:7-21bpCONTAINS ONE OR TWO UNINERRUPTED ORFs

EXAMPLES:IS ELEMENTSTn ELEMENTS

EXAMPLES:Ac/Ds ELEMETSP ELEMTS

EXAMPLES:Ty1copia

EXAMPLES:F, G, I ELEMENTSLINES AND SINES

The movement of a transposable element from one location to anotherAll types of transposition have several features in common:

(1) staggered breaks are made in the target DNA

(2) The transposable element is joined to single-stranded ends of the target DNA

(3) DNA is replicated at the single strand gaps

Transposable elements Retroelements

mRNA

PROPERTIES BACTERIAL TRANSPOSASE RETROVIRAL INTERGASASE

INSERTION EVENT CHEMICALLY IDENTICAL

SEQUENCE SIMILARITY CERTAIN AMINO ACIDS ARE SIMILER IN BOTH ENZYMES AT THE ACTIVE SITE CALLED, DDE MOTIF

END RECOGNITION SEQUENCE SELECTIVITY IN BINDING

LITTLE OR NO SEQUENCE SELECTIVITY IN BINDING

STRAND CLEVAGE CAN CLEAVE SINGLE STRAND OR DOUBLE STRAND OR CAN CREATE INTERMEDIATES CARRYING OVERHANGS

ONLY CLEAVES SINGLE STRAND

STRAND TRANSFER THE TERMINAL SEQUENCES MAY OR MAY NOT INFLUENCE THE STRAND TRANSFER

THE TERMINAL NUCLEATIDES, WHICH ARE ELIMINATED IN THE INTEGRATED PROVIRUS INFLUENCE THE STRAND TRANSFER

Polard &Chandle’ Bacterialtransposases and retroviral integrases’, Molecular Microbiology (1995) 15(1), 13-23

Insertion sequencesCarries only the genetic information necessary for its movementConstituents of bacteria and plasmids800 to 2000 bpCut-and-paste transposonsTerminal inverted repeatsThe generation of flanking direct repeats at the site of insertion

Composite transposonsAny segment of DNA that becomes flanked by two copies of an insertion sequence may itself transpose and is called a composite transposon.Terminal inverted repeatsGenerate flanking direct repeats at their sites of insertion

Noncomposite transposonslack insertion sequences5000 bp longTerminal inverted repeats of 38 bpGenerates flanking direct repeats of5 bpCarries genes for transposase and resolvase plus a gene that codes for the enzyme -lactamase, which provides resistance to ampicillin.

Transposing bacteriophagesGenerate short (5-bp) flanking direct repeatsMu replicates through transpositionLike the TE they causes mutations at the site of insertion

Variation at sub genomic level:Variation mediated by excisions and transposes-mediated deletionsVariations mediated by insertionsSterility associated with hybrid dysgenesis

Variation at genomic level:Non random distribution and genome partitioningTE and genome size

Transposons induced variation and host evolutionGermline restriction of transpositionHost responses: epigentic regulation of TE

Transposable elements may create genetic diversity Act as promoters Allow recombination between plasmid and genomic DNA

when multiple copies of the element are present Carry antibiotic resistance genes, conferring an

advantage on bacterial cells Increase the number of copies of an exon or gene

Gene taggingTransposon trapsChromosomal rearrengementsActivation taggingReverse genetic screening

Retroviral vectors are useful for animal transformationInsertional Mutagenesis for Gene IdentificationVector Insertion as a Marker for Gene Activity during DevelopmentTransfer of Genes That Regulate Development in AnimalsChromosome TaggingShuttle VectorsCellular Immortalization

BOOKS1.Genetics A conceptual Approach (2nd edition)Benjamin Pierce2.Lewin’s essential GENES (3rd edition)J.Krebs, E.Goldstein, S.Kilpatrick3.Mobile DNA 2Edited by: N.Cradig, R.Craigie, M.Gellert, A.Lambowitz

RESEARCH PAPERS1.C. Kumar, K. Narayana ‘Plant transposable elements and functional genomics’, Plant Biotechnology(1998) 15(4), 159-1652.P.Polard , M.Chandler ‘Bacterial transposases and retroviral integrases’ Molecular Microbiology(1995) 15(1),13-233. P.Rice , T.Baker ‘Comparative architecture of transposase and integrasecomplexes’nature structural biology ,Volume 8 number 4 ,April 20014. Martín Muñoz-López and José L. García-Pérez ‘DNA Transposons: Nature and Applications in Genomics’ Current Genomics, 2010, 11, 115-1285. C. Feschotte,N. Jiang and S.Wessler,’ Plant transposable elements:where genetics meets genomics’ Nature Reviews ,Genetics,volume 3 ,may 2002 ,329-3416. A D Miller ‘Development and Applications of Retroviral Vectors’ www.ncbi.nlm.nih.gov › NCBI › Literature › Bookshelf