Résumé
Many genetic rearrangements occur through recombination between short repeated sequences. Among these changes, deletions lead to a loss of genetic information and the bringing together of sequences that are usually far apart. This can result in the inactivation or activation of certain functions. Excision of the mini tn10 transposon is a deletion event occurring between the direct repeats created when this element is inserted into the target sequence. This transposase-independent event has been used as a tool to study the factors affecting the frequency of deletions and the mechanism leading to their formation. Both precise and imprecise excisions of mini tn10 (involving direct repeats of 9 base pairs or imperfect repeats of 24 base pairs, respectively) are stimulated when the transposon is carried by a derivative of pbr322 containing the origin of m13 upon infection of bacteria with m13 or the apparent phage f1. The phenomenon is rapid and efficient. Stimulation of excision requires activation of the rolling circle replication initiated at the origin of m13 by phage replication proteins ii (the protein responsible for initiation and m13 by phage replication proteins ii (the protein responsible for initiation and termination) and v (the protein that binds to single-stranded dna). It also requires helicase rep encoded by escherichia coli, which is necessary for the elongation of the replication of phage m13. Activation of another origin of circle-rolling replication, that of pc194, a replicative gram-positive bacterial plasmid in escherichia coli, does not stimulate excision of a palindromic structure framed by direct repeats of 18 base pairs. The molecular mechanism models known for this type of rearrangement are either conservative (break and reunite) or non-conservative (copy choice). In order to decide between these two types of model, we measured the transfer of heavy atoms from parent molecules to recombinant molecules. We were able to show that the recombinant molecules formed when rolling-circle replication is induced do not inherit any parental nucleotide material, and therefore result from a copy-choice recombination mechanism.