A mutation in helicase motif III of E. coli RecG protein abolishes branch migration of Holliday junctions

Nucleic Acids Res. 1994 Feb 11;22(3):308-13. doi: 10.1093/nar/22.3.308.


The RecG protein of Escherichia coli catalyses branch migration of Holliday junctions made by RecA and dissociates synthetic X junctions into duplex products in reactions that require hydrolysis of ATP. To investigate the mode of action of this enzyme a chromosomal mutation that inactivates recG (recG162) was cloned and sequenced. The recG162 mutation is a G:C to A:T transition, which produces an Ala428 to Val substitution in the protein. This change affects a motif (motif III) in the protein that is highly conserved in DNA and RNA helicases. RecG162 protein was purified and shown to retain the ability to bind synthetic X and Y junctions. However, it does not dissociate these junctions and fails to catalyse branch migration of Holliday junction intermediates purified from a RecA strand exchange reaction. RecG162 retains a DNA-dependent ATPase activity, but this is much reduced relative to the wild-type protein, especially with single-stranded DNA as a co-factor. These results suggest that branch migration by RecG is related to a junction-targeted DNA helicase activity.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphatases / genetics
  • Adenosine Triphosphatases / metabolism
  • Amino Acid Sequence
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Base Sequence
  • DNA Helicases / genetics
  • DNA Helicases / metabolism*
  • DNA Primers / chemistry
  • DNA Repair
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Escherichia coli / enzymology*
  • Escherichia coli / radiation effects
  • Escherichia coli Proteins*
  • Genes, Bacterial
  • Molecular Sequence Data
  • Recombination, Genetic*
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Ultraviolet Rays


  • Bacterial Proteins
  • DNA Primers
  • DNA-Binding Proteins
  • Escherichia coli Proteins
  • RecG protein, E coli
  • Adenosine Triphosphatases
  • DNA Helicases