Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Fig 13-1Chapter 13: transposable elementsFig 13-8Multiple IS elements can exist at diverse sitesin bacterial chromosomes and plasmidsExample: IS elements in an F factorVarious classes of Insertion Sequence (IS) elements have been identified in E. coliElement-specific inverted DNA sequence repeats flank each elementFig 13-9Transposons may be elaborate IS-type elements (simple)or DNA fragments with IS elements at each endFig 13-10Individual plasmids can contain multiple transposonscarrying multiple resistance genesMobility of the transposons provides extensive mobility of the R factorsFig 13-11Insertion of a bacterial transposons usually involves duplication of DNA sequences flanking the insertion siteResembles restrictionendonuclease cutFig 13-12Two modes of transposition of a bacterial transposonsFig 13-13Replicative transposition involves cointegrate intermediateFig 13-14One class of eukaryote transposable elements (retrotransposons)appear to be related to retrovirusesRetrovirus life cycleFig 13-15Examples ofeukaryoteretrotransposonsAll contain vestiges of retroviral genesmost retain polFig 13-16Retrotransposons such as yeast Ty1transpose through an RNA intermediateFig 13-21The first transposon system identified:Ac-Ds system in corn(B. McClintock)Ac transposase can mobilize more than one transposonFig 13-18Drosophila P elements were discoveredby study of a hybrid dysgenesis syndromeFig 13-19P-M dysgenesis is due to presence of the P element transposon in P fliesFig 13-19P-M dysgenesis is due to presence of the P element transposon in P fliesFig 13-20Mobilization limited to germline cells:• Normal development of somatic tissue• degenerate germ cells due to massive genetic damageFig 13-22P element has been engineered as a transformation vectorFig 13-23Up to ½ of human genome is transposable elements and residuesFig 13-24The human HGO gene contains numerous repetitive elementsAll elements are within introns(exon insertions are presumably subject to negative selection)Many mutations are caused by insertionsof transposable genetic elementsFig 13-25Retrotransposon abundance accounts for enormous differences in genome sizes in different grassesFig 13-Some transposons display insertion site specificitiesthat promote their accumulation in “safe havens”Fig 13-Fig