Modulating cellular recombination potential through alterations in RecA structure and regulation.

The wild-type Escherichia coli RecA protein is a recombinase platform with unrealized recombination potential. We have explored the factors affecting recombination during conjugation with a quantitative assay. Regulatory proteins that affect RecA function have the capacity to increase or decrease recombination frequencies by factors up to sixfold. Autoinhibition by the RecA C-terminus can affect recombination frequency by factors up to fourfold. The greatest changes in recombination frequency measured here are brought about by point mutations in the recA gene. RecA variants can increase recombination frequencies by more than 50-fold. The RecA protein thus possesses an inherently broad functional range. The RecA protein of E. coli (EcRecA) is not optimized for recombination function. Instead, much of the recombination potential of EcRecA is structurally suppressed, probably reflecting cellular requirements. One point mutation in EcRecA with a particularly dramatic effect on recombination frequency, D112R, exhibits an enhanced capacity to load onto SSB-coated ssDNA, overcome the effects of regulatory proteins such as PsiB and RecX, and to pair homologous DNAs. Comparisons of key RecA protein mutants reveal two components to RecA recombination function - filament formation and the inherent DNA pairing activity of the formed filaments.