Abstract
The RecX protein of Escherichia coli inhibits the extension of RecA protein filaments on DNA, presumably by binding to and blocking the growing filament end. The direct binding of RecX protein to single-stranded DNA is weak, and previous reports suggested that direct binding to DNA did not explain the effects of RecX. We now demonstrate that elevated concentrations of SSB greatly moderate the effects of RecX protein. High concentrations of the yeast RPA protein have the same effect, suggesting that the effect is not species-specific or even specific to bacterial SSB proteins. A direct SSB-RecX interaction is thus unlikely. We suggest that SSB is blocking access to single-stranded DNA. The evident competition between RecX and SSB implies that the mechanism of RecX action may involve RecX binding to both RecA protein and to DNA. We speculate that the interaction of RecX protein and RecA may enable an enhanced DNA binding by RecX protein. The effects of SSB are increased if the SSB C terminus is removed.
Highlights
The assembly and disassembly of RecA protein filaments on DNA has been studied in some detail, understanding is not complete
SSB Protein Antagonizes RecX Function—In the absence of SSB protein, the ATP hydrolysis rate was constant and slow. This reflects the limited binding of RecA to the single-stranded DNA (ssDNA), where formation of a complete and contiguous RecA filament is precluded by secondary structure in the DNA
We conclude that SSB antagonizes the inhibitory effects of RecX protein on RecA protein filaments
Summary
Intact RecA filament, it spans the monomer-monomer interface, binding from the C-terminal domain of one RecA monomer to the core domain of a second monomer [59]. The RecX protein is effective in halting RecA filament extension, and a previous study suggested that RecX acts via a capping mechanism [52]. The binding of RecX to the growing end of a RecA filament would preclude further RecA protein additions at that end [52]. The apparently weak binding of RecX to ssDNA suggested that RecX did not bind to the DNA and act as an inert barrier to extension but instead interacted directly with the RecA protein. The function of RecX binding elsewhere along the RecA filament is unclear. The patterns of interference indicate a direct competition between SSB and RecX for a ligand, presumably ssDNA, and suggest that an interaction of RecX with ssDNA may be part of the mechanism by which RecX halts RecA filament extension. The RecXssDNA interaction may be affected by RecA protein and underestimated in the earlier work
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
