A unique beta-hairpin protruding from AAA(+) ATPase domain of RuvB motor protein is involved in the interaction with RuvA DNA recognition protein forbranch migration of Holliday junctions

The Escherichia coh RuvB protein is a motor protein that forms a complex wi th RuvA and promotes branch migration of Holliday junctions during homologo us recombination. This study describes the characteristics of two RuvB muta nts, I148T and I150T, that do not promote branch migration in the presence of RuvA. These RuvB mutants hydrolyzed ATP and bound duplex DNA with the sa me efficiency as wild-type RuvB, but the mutants did not form a complex wit h RuvA and were defective in loading onto junction DNA in a RuvA-assisted m anner. A recent crystallographic study revealed that Ile(148) and Ile(150) are in a unique beta -hairpin that protrudes from the AAA(+) ATPase domain of RuvB. We propose that this beta -hairpin interacts with hydrophobic resi dues in the mobile third domain of RuvA and that this interaction is vital for the RuvA-assisted loading of RuvB onto Holliday junction DNA.