Efficient Strand Transfer by the RadA Recombinase from the Hyperthermophilic Archaeon Desulfurococcus amylolyticus

TheradA gene predicted to be responsible for homologous recombination in a hyperthermophilic archaeon,Desulfurococcus amylolyticus , was cloned, sequenced, and overexpressed inEscherichia coli cells. The deduced amino acid sequence of the gene product, RadA, was more similar to the human Rad51 protein (65% homology) than to theE. coli RecA protein (35%). A highly purified RadA protein was shown to exclusively catalyze single-stranded DNA-dependent ATP hydrolysis, which monitored presynaptic recombinational complex formation, at temperatures above 65°C (catalytic rate constant of 1.2 to 2.5 min−1 at 80 to 95°C). The RadA protein alone efficiently promoted the strand exchange reaction at the range of temperatures from 80 to 90°C, i.e., at temperatures approaching the melting point of DNA. It is noteworthy that both ATP hydrolysis and strand exchange are very efficient at temperatures optimal for host cell growth (90 to 92°C).