Chapter 13: transposable elements Fig 13-1

Multiple IS elements can exist at diverse sites in bacterial chromosomes and plasmids Example: IS elements in an F factor Fig 13-8

Various classes of Insertion Sequence (IS) elements have been identified in E. coli Element-specific inverted DNA sequence repeats flank each element

Transposons may be elaborate IS-type elements (simple) or DNA fragments with IS elements at each end Fig 13-9

Individual plasmids can contain multiple transposons carrying multiple resistance genes Mobility of the transposons provides extensive mobility of the R factors Fig 13-10

Insertion of a bacterial transposons usually involves duplication of DNA sequences flanking the insertion site Resembles restriction endonuclease cut Fig 13-11

Two modes of transposition of a bacterial transposons Fig 13-12

Replicative transposition involves cointegrate intermediate Fig 13-13

One class of eukaryote transposable elements (retrotransposons) appear to be related to retroviruses Retrovirus life cycle Fig 13-14

All contain vestiges of retroviral genes Examples of eukaryote retrotransposons All contain vestiges of retroviral genes most retain pol Fig 13-15

Retrotransposons such as yeast Ty1 transpose through an RNA intermediate Fig 13-16

The first transposon system identified: Ac-Ds system in corn (B. McClintock) Ac transposase can mobilize more than one transposon Fig 13-21

Drosophila P elements were discovered by study of a hybrid dysgenesis syndrome Fig 13-18

P-M dysgenesis is due to presence of the P element transposon in P flies Fig 13-19

P-M dysgenesis is due to presence of the P element transposon in P flies Fig 13-19 Mobilization limited to germline cells: Normal development of somatic tissue degenerate germ cells due to massive genetic damage Fig 13-20

P element has been engineered as a transformation vector Fig 13-22

Up to ½ of human genome is transposable elements and residues Fig 13-23

The human HGO gene contains numerous repetitive elements All elements are within introns (exon insertions are presumably subject to negative selection) Fig 13-24

Many mutations are caused by insertions of transposable genetic elements

Retrotransposon abundance accounts for enormous differences in genome sizes in different grasses Fig 13-25

Some transposons display insertion site specificities that promote their accumulation in “safe havens” Fig 13-

Fig 13-

Fig 13-