recA-independent general genetic recombination of plasmids

Abstract

The small circular genomes of several bacteriophages and a number of plasmids have been used extensively to study various aspects of the mechanism of genetic recombination. Several studies have demonstrated that the interconversion between the circular monomers and larger circular oligomers of many plasmid DNAs is mediated, at least in part, by the pathway which carries out genetic recombination in wild-type Escherichia coli^1–4. The recA, recB and recC mutations block conjugation-mediated recombination in E. coli^5,6. However, Clark and his co-workers^7,8 isolated two mutations, sbcA and sbcB, which indirectly suppress the recombination deficiency of recB and recC mutations. These indirect suppressor mutations seem to cause recombination by other pathways which require the recA gene product as well as products of other genes such as recF, recJ and recM, which are not normally required for recombination in E. coli^9,10. Here we report an investigation of the effect of recombination-deficient mutations on plasmid recombination in E. coli. We show that sbcA mutations induce a new plasmid recombination pathway that is 10–15 times more efficient than the normal wild-type recombination pathway and independent of the recA and recF functions.