TRANSPOSITION AND SITE-SPECIFIC RECOMBINATION - ADAPTING DNA CUT-AND-PASTE MECHANISMS TO A VARIETY OF GENETIC REARRANGEMENTS

In bacteria, two categories of specialised recombination promote a var iety of DNA rearrangements. Transposition is the process by which gene tic elements move between different locations of the genome, whereas s ite-specific recombination is a reaction in which DNA strands are brok en and exchanged at precise positions of two target DNA loci to achiev e determined biological function. Both types of recombination are repr esented by diverse genetic systems which generally encode their own re combination enzymes. These enzymes, generically called transposases an d site-specific recombinases, can be grouped into several families on the basis of amino acid sequence similarities, which, in some cases, a re limited to a signature of a few residues involved in catalysis. The well characterised site-specific recombinases are found to belong to two distinct groups, whereas the transposases form a large super-famil y of enzymes encompassing recombinases from both prokaryotes and eukar yotes. In spite of important differences in the catalytic mechanisms u sed by these three classes of enzymes to cut and rejoin DNA molecules, similar strategies are used to coordinate the biochemical steps of th e recombination reaction and to control its outcome. This review summa rises our current understanding of transposition and site-specific rec ombination, attempting to illustrate how relatively conserved DNA cut- and-paste mechanisms can be used to bring about a variety of complex D NA rearrangements.