MUTATIONAL ANALYSIS OF A SITE-SPECIFIC RECOMBINASE - CHARACTERIZATIONOF THE CATALYTIC AND DIMERIZATION DOMAINS OF THE BETA-RECOMBINASE OF PSM19035

The beta recombinase encoded by the streptococcal plasmid pSM19035, wh ich shows 28 to 34% identity with DNA resolvases and DNA invertases, c an catalyze formation of deletions or inversions between properly orie nted target sites. We have constructed a number of site-directed mutat ions at residues that are conserved between the beta protein and other DNA recombinases of the resolvase/invertase family. The analysis of t he recombination and DNA-binding ability of each mutant protein shows that the mutations affect the catalytic activity and, in two cases, th e dimerization of the protein. The results suggest that the beta prote in probably mediates recombination by a catalytic mechanism similar to that proposed for the resolvase/invertase family. Since the beta reco mbinase differs from DNA resolvases and DNA invertases in its lack of bias towards either of these reactions, the results presented support the hypothesis that its unique properties might depend on details of t he architecture or assembly of the recombination complex. In addition, two beta protein mutants that can no longer form dimers in solution h ave provided new insights into the way the protein binds to DNA.