DNA Site-Specific Resolution Systems

Resolution of multimeric forms of circular plasmids and chromosomes is mediated by site-specific recombination, an efficient and tightly controlled DNA breakage and joining reaction occurring at the level of determined DNA sequences. Site-specific recombinases, the enzymes that catalyze this type of reaction, fall into two families of proteins: the serine-recombinase and tyrosine-recombinase families. The chapter discusses the mechanisms that generate DNA multimers and their consequence on the segregational stability of bacterial replicons, and also provides an overview of the variety of site-specific resolution systems found on circular plasmids and chromosomes and their relationship to other recombination systems. It focuses on site-specific resolution systems of the serine-recombinase family, and plasmid and chromosome resolution systems of the tyrosine recombinase family. The topology of the recombination reaction catalyzed by other resolvases of the serine-recombinase family, such as the ParA protein of RP4/RK2, the resolvase of ISXc5, the Sin recombinase of Staphylococcus aureus, and the β recombinase of pSM19035, was found to be identical to that reported for the cointegrate resolution system of Tn3-family transposons. Studies on plasmid and transposon resolution systems provide fascinating examples of convergent evolution, in which structurally and biochemically unrelated molecular machines have been adapted to bring about functionally similar DNA rearrangements in an exquisitely controlled manner.