Escherichia coli RecG and RecA proteins in R-loop formation

EMBO J. 1995 May 15;14(10):2385-92.


Escherichia coli rnhA mutants devoid of RNase HI exhibit constitutive stable DNA replication, cSDR, which is thought to be initiated from R-loops stabilized in the absence of RNase HI. We found that a combination of an rnhA and a recG mutation is lethal to the cell. recG mutations that inactivate the helicase activity of RecG protein and inhibit reverse branch migration of Holliday junctions impart phenotypes resembling those of rnhA mutants. Thus, recG mutants display cSDR activity, and recG polA double mutants are inviable as are rnhA polA double mutants. These results suggest that the RecG helicase has a role in preventing R-loop formation. A model that R-loops are formed by assimilation of RNA transcripts into the duplex DNA is discussed. The model further postulates that RecA protein catalyzes this assimilation reaction and that RecG protein counteracts RecA in this reaction, resolves R-loops by its helicase activity, or does both.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • DNA Helicases / genetics
  • DNA Helicases / metabolism*
  • DNA Polymerase I / genetics
  • DNA Repair
  • DNA Replication / genetics*
  • DNA, Bacterial / biosynthesis
  • DNA-Binding Proteins / genetics
  • Escherichia coli / genetics*
  • Escherichia coli Proteins*
  • Genes, Bacterial / genetics
  • Genes, Lethal / genetics
  • Kanamycin Resistance / genetics
  • Models, Genetic
  • Mutation
  • Nucleic Acid Conformation
  • Nucleic Acid Heteroduplexes
  • Rec A Recombinases / metabolism*
  • Recombination, Genetic
  • Replication Origin
  • Ribonuclease H / analysis
  • Ribonuclease H / genetics
  • SOS Response, Genetics
  • Sequence Analysis, DNA


  • Bacterial Proteins
  • DNA, Bacterial
  • DNA-Binding Proteins
  • DnaA protein, Bacteria
  • Escherichia coli Proteins
  • Nucleic Acid Heteroduplexes
  • RecG protein, E coli
  • DNA Polymerase I
  • Rec A Recombinases
  • Ribonuclease H
  • ribonuclease HI
  • DNA Helicases