The ATP Hydrolysis Cycle and the Corresponding Motion of RecA Filament on Single-Stranded DNA

Abstract

RecA is involved in DNA repair mechanism in bacteria by catalyzing homologous strand exchange reaction. RecA forms a filament on a single-stranded DNA made at the double-strand breaks. RecA adopts either a stretched (active) structure with ATP as a cofactor, or a compressed (inactive) structure with ADP. At the filament end, a monomer is allowed to dissociate after ATP hydrolysis and to rebind. We developed a single-molecule fluorescence assay to investigate how the ATP hydrolysis is coupled with the dynamics of the RecA filament. We dissected the intermediate steps of ATP hydrolysis and discovered that a monomer at the filament end dissociated upon the hydrolysis of ATP and not after the release of Pi. Interconversion of the structure between stretched- and compressed forms was achieved via cooperative structural change of a group of neighboring monomers. Owing to this cooperativity, an internal RecA monomer continuously consumes and rapidly refreshes ATP molecule without changing its stretched conformation. Based on our observation, we suggest a model of ATP hydrolysis cycle of the RecA in the filament.