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