Inhibition of RecA protein by the Escherichia coli RecX protein: modulation by the RecA C terminus and filament functional state.

The RecX protein is a potent inhibitor of RecA activities. We identified several factors that affect RecX-RecA interaction. The interaction is enhanced by the RecA C terminus and by significant concentrations of free Mg(2+) ion. The interaction is also enhanced by an N-terminal His(6) tag on the RecX protein. We conclude that RecX protein interacts most effectively with a RecA functional state designated A(o) and that the RecA C terminus has a role in modulating the interaction. We further identified a C-terminal point mutation in RecA protein (E343K) that significantly alters the interaction between RecA and RecX proteins.