Exchange of recA protein between adjacent recA protein-single-stranded DNA complexes

We have examined the exchange of recA protein between stable complexes formed with single-stranded DNA (ssDNA) and (a) other complexes and (b) a pool of free recA protein. We have also examined the relationship of ATP hydrolysis to these exchange reactions. Exchange was observed between two different recA X ssDNA complexes in the presence of ATP. Complete equilibration between two sets of complexes occurred with a t1/2 of 3-7 min under a set of conditions previously found to be optimal for recA protein-promoted DNA strand exchange. Approximately 200 ATPs were hydrolyzed for every detected migration of a recA monomer from one complex to another. This exchange occurred primarily between adjacent complexes, however. Little or no exchange was observed between recA X ssDNA complexes and the free recA protein pool, even after several hundred molecules of ATP had been hydrolyzed for every recA monomer present. ATP hydrolysis is not coupled to complete dissociation or association of recA protein from or with recA X ssDNA complexes under these conditions.