Characterization of Staphylococcus aureus RecX protein: Molecular insights into negative regulation of RecA protein and implications in HR processes.

Homologous recombination (HR) is essential for genome stability and for maintaining genetic diversity. In eubacteria, RecA protein plays a key role during DNA repair, transcription, and HR. RecA is regulated at multiple levels, but majorly by RecX protein. Moreover, studies have shown RecX is a potent inhibitor of RecA and thus acts as an antirecombinase. Staphylococcus aureus is a major food-borne pathogen that causes skin, bone joint, and bloodstream infections. To date, RecX's role in S. aureus has remained enigmatic. Here, we show that S. aureus RecX (SaRecX) is expressed during exposure to DNA-damaging agents, and purified RecX protein directly interacts physically with RecA protein. The SaRecX is competent to bind with single-stranded DNA preferentially and double-stranded DNA feebly. Significantly, SaRecX impedes the RecA-driven displacement loop and inhibits formation of the strand exchange. Notably, SaRecX also abrogates adenosine triphosphate hydrolysis and abolishes the LexA coprotease activity. These findings highlight the role of the RecX protein as an antirecombinase during HR and play a pivotal role in regulation of RecA during the DNA transactions.