The in vitro activity of a Rad55 homologue from Sulfolobus tokodaii, a candidate mediator in RadA-catalyzed homologous recombination.

Archaea have recombination proteins similar to those of eukaryote, but many have not been characterized. Here, the characterization of a Rad55 homologue from Sulfolobus tokodaii (stRad55A) was reported. StRad55A protein preferred binding to ssDNA and had ssDNA-dependent ATPase activity. In addition, UV light could induce the expression of this protein, which was different from RadB, a RadA paralog found in euryarchaeota. Most importantly, stRad55A could release the suppression of excessive stSSB (single strand DNA binding protein from S. tokodaii) on the strand exchange catalyzed by stRadA (RadA homologue from S. tokodaii), by interacting directly with both stRadA and stSSB. StRad55A may function as a mediator to accelerate the displacement of stSSB by stRadA.