A recombinational defect in the C‐terminal domain of Escherichia coli RecA2278‐5 protein is compensated by protein binding to ATP

RecA2278‐5 is a mutant RecA protein (RecAmut) bearing two amino acid substitutions, Gly‐278 to Thr and Val‐275 to Phe, in the α‐helix H of the C‐terminal sub‐domain of the protein. recA2278‐5 mutant cells are unusual in that they are thermosensitive for recombination but almost normal for DNA repair of UV damage and the SOS response. Biochemical analysis of purified RecAmut protein revealed that its temperature sensitivity is suppressed by prior binding of this protein to its ligand. In fact, the preheating of RecAmut protein for several minutes at a restrictive temperature (42°C) in the absence of ATP resulted in inhibition at 42°C of many activities related to homologous recombination including ss‐ and dsDNA binding, high‐affinity binding for ATP, ss‐ or dsDNA‐dependent ATPase, RecA–RecA interaction, and strand transfer capability. The binary complex RecAmut::ATP under the same conditions showed a decrease in only two activities, i.e. dsDNA binding and high‐affinity binding for ATP. Besides ATP, sodium acetate (1.5M) was shown to be another factor that can stabilize the RecAmut protein at 42°C, judging by restoration of its DNA‐free ATPase activity. The similarity of influence of high salt (with its non‐specific binding) and ATP (binding specifically) on the apparent protein folding stability suggests that the structural stability of the RecA C‐terminal domain is one of the conditions for correct interaction between RecA protein and ATP in the RecA::ATP::ssDNA presynaptic complex formation. The decrease in affinity for ATP was suggested to be the factor that determined a particular recombinational (but not repair) thermosensitivity of the RecAmut protein. Finally, we show that the stability of C‐terminal domain appeared to be necessary for the dsDNA‐binding activity of the protein.