Eukaryotic transposable elements

Abstract

Transposable elements first discovered in maize have been discovered subsequently also in bacteria, yeast, Drosophila, mammals etc. Structurally, eukaryotic transposable elements may be classified into two groups: ones with direct or inverse-repeat ends and the others with dAMP-rich sequence at one end. They generate direct repeats at the target site. Quite often, transposable elements are dispersed as a number of copies through the genome and at times may constitute a small but significant fraction. Their dispersal or transposition through the genome may involve excision (precise or imprecise), recombination (homologous or non-homologous) and replicative events in elements with direct or inverse repeats. dAMP-ended elements may move by reverse transcription. Maize elements can modulate gene action and yeast Tyl elements can enhance transcription. Nevertheless, evidence is not conclusive that transposable elements are involved in a major way in gene regulation and development. Structural similarities among yeast Tyl elements,Drosophila copia sequences and retroviral proviruses such as Rous sarcoma virus (RSV) and mouse mammary tumor virus (MMTV) suggest a formal possibility of horizontal transfers.