[Transposition as a way of existence: phage Mu]

Abstract

Transposition is a special mode of DNA recombination that produces a transfer of a DNA segment (transposable element, TE) from one chromosome region to a nonhomologous genomic loci. Bacterial TEs have chosen two principal strategies of their movement within and among genomes: conservative transposition (resulting in a simple insertion) and/or replicative transposition (accompanied by complete DNA replication and producing a cointegrate). Variations of transposition strategies concern the number and nature of cuts that sever the transposon from the flanking donor DNA: one-strand break (phage Mu) or double-strand breaks (Tn7, IS10 and members of IS3 family) and the possibility of accompanying TE replication, which leads to different end-products of transposition. Phage Mu combines properties of a temperate phage and a transposable element. Among transposons, it is studied in most detail. As a transposable element phage Mu is remarkable because its life-cycle involves two transposition modes: non-replicative resulting in lysogeny and replicative leading to multiple copying of phage DNA during the lytic growth. There are several levels of transcription regulation (or choice of developmental pathway). The genetic transposition reaction mediated by phage Mu A transposase A in the transpososome complex involves elaborate protein-nucleic acid and protein-protein interactions.