Roles of Bacillus subtilis DprA and SsbA in RecA-mediated Genetic Recombination [Microbiology]

August 19th, 2014 by Yadav, T., Carrasco, B., Serrano, E., Alonso, J. C.

Bacillus subtilis competence-induced RecA, SsbA, SsbB and DprA are required to internalize and to recombine single-stranded (ss) DNA with homologous resident duplex. RecA, in the ATP-Mg2+ bound form (RecA-ATP), can nucleate and form filament onto ssDNA, but inactive to catalyze DNA recombination. We report that SsbA or SsbB bound to ssDNA blocks the RecA filament formation, and fail to activate recombination. DprA facilitates RecA filamentation, however the filaments cannot engage in DNA recombination. When ssDNA was pre-incubated with SsbA, but not SsbB, DprA was able to activate DNA strand exchange dependent on RecA-ATP. This work demonstrates that RecA-ATP, in concert with SsbA and DprA, catalyzes DNA strand exchange, and SsbB is an accessory factor in the reaction. In contrast, RecA-dATP efficiently catalyzes strand exchange even in the absence of SSBs or DprA, and addition of the accessory factors marginally improved it. We proposed that the RecA bound nucleotide (ATP and to a lesser extent dATP) might dictate the requirement for accessory factors