Dynamic growth and shrinkage govern the pH dependence of RecA filament stability.

Sung Hyun Kim,Chirlmin Joo,Doseok Kim,Taekjip Ha,Jeehae Park

doi:10.1371/journal.pone.0115611

Abstract

RecA proteins form a long stable filament on a single-stranded DNA and catalyze strand exchange reaction. The stability of RecA filament changes dramatically with pH, yet its detailed mechanism is not known. Here, using a single molecule assay, we determined the binding and dissociation rates of RecA monomers at the filament ends at various pH. The pH-induced rate changes were moderate but occurred in opposite directions for binding and dissociation, resulting in a substantial increase in filament stability in lower pH. The highly charged residues in C-terminal domain do not contribute to the pH dependent stability. The stability enhancement of RecA filament in low pH may help the cell to cope with acidic stress by fine-tuning of the binding and dissociation rates without losing the highly dynamic nature of the filament required for strand exchange.

Highlights

RecA protein is essential for repairing damaged chromosomal DNA by mediating homologous recombination [1,2,3]
Acid tolerance is vital to E. coli as it needs to pass through the acidic stomach of vertebrate
In our previous report [9], we have shown that the binding rate at the 3’ end is much higher than the dissociation rate at physiological concentration of RecA, whereas the binding and the dissociation rates are comparable at the 5’ end

Summary

Introduction

RecA protein is essential for repairing damaged chromosomal DNA by mediating homologous recombination [1,2,3]. A recent single molecule study reported enhancement in both initial nucleation and consequent growth rates of a filament at low pH, suggesting that pH may affect both binding and dissociation processes [17]. PH-dependent enhancement of nucleation of RecA proteins on a dsDNA was observed in another single-molecule manipulation study [18], yet the details of the RecA dynamics at the filament ends at high resolution are still missing.

Results

Conclusion