RUVA AND RUVB PROTEINS OF ESCHERICHIA-COLI EXHIBIT DNA HELICASE ACTIVITY INVITRO

The SOS-inducible ruvA and ruvB gene products of Escherichia coli are required for normal levels of genetic recombination and DNA repair. In vitro, RuvA protein interacts specifically with Holliday junctions and, together with RuvB (an ATPase), promotes their movement along DNA. This process, known as branch migration, is important for the formation of heteroduplex DNA. In this paper, we show that the RuvA and RuvB proteins promote the unwinding of partially duplex DNA. Using single-stranded circular DNA substrates with annealed fragments (52-558 nucleotides in length), we show that RuvA and RuvB promote strand displacement with a 5'--> 3' polarity. The reaction is ATP-dependent and its efficiency is inversely related to the length of the duplex DNA. These results show that the ruvA and ruvB genes encode a DNA helicase that specifically recognizes Holliday junctions and promotes branch migration.