Drosophila Transposable Elements
Bacterial Transposable Elements
Bacterial Transposable Elements
Bacterial transposable elements were initially detected because of the genetic instability of phenotypes. Molecular analysis of transposable elements was first performed with bacterial elements and these results formed the basis for hypothesis about eukaryotic elements. The two classes of bacterial elements are insertion sequences or IS elements and Tn elements. Both of these classes are related to each other. IS elements are a family of elements that range from 768 to 1426 bp in size and are represented in different copy number in bacterial chromosomes and on associated F factors.
| Element | # in E. coli | # in F factor |
|---|---|---|
| IS1 | 8 | - |
| IS2 | 5 | 1 |
| IS3 | 1 | 2 |
| IS4 | 1 | - |
Features of IS and Tn elements
- inverted repeats on each end of the element that range in size from 9-40 bp
- create duplications of the target site upon insertion; this duplication occurs at both ends of the elements and they are in a direct orientation
- composite transposons (Tns) can be created when two IS elements insert near each other; if the terminal repeats are used for further transposition then the internal sequences will be carried along
- Tns arise from IS elements; these may be identical or different IS elements; Tn5 is derived from IS50L and IS50R; these two elements differ by a single nucleotide change in IS50L which has eliminated its transposition ability
- the IS elements contain two genes that are essential for transposition, a transposase and a resolvase; the transposition functions in Tns are found in the IS region of the element
- Tns normally carry a drug resistance gene