ATP-dependent resolution of R-loops at the ColE1 replication origin by Escherichia coli RecG protein, a Holliday junction-specific helicase

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Abstract
The RecG protein of Escherichia coli is a DNA helicase that promotes branch migration of the Holliday junctions. We found that overproduction of RecG protein drastically decreased copy numbers of ColE1‐type plasmids, which require R‐loop formation between the template DNA and a primer RNA transcript (RNA II) for the initiation of replication. RecG efficiently inhibited in vitro ColE1 DNA synthesis in a reconstituted system containing RNA polymerase, RNase HI and DNA polymerase I. RecG promoted dissociation of RNA II from the R‐loop in a manner that required ATP hydrolysis. These results suggest that overproduced RecG inhibits the initiation of replication by prematurely resolving the R‐loops formed at the replication origin region of these plasmids with its unique helicase activity. The possibility that RecG regulates the initiation of a unique mode of DNA replication, oriC ‐independent constitutive stable DNA replication, by its activity in resolving R‐loops is discussed.