The arginine finger of bacteriophage T7 gene 4 helicase: role in energy coupling

Proc Natl Acad Sci U S A. 2004 Mar 30;101(13):4373-8. doi: 10.1073/pnas.0400968101.


The DNA helicase encoded by gene 4 of bacteriophage T7 couples DNA unwinding to the hydrolysis of dTTP. The loss of coupling in the presence of orthovanadate (Vi) suggests that the gamma-phosphate of dTTP plays an important role in this mechanism. The crystal structure of the hexameric helicase shows Arg-522, located at the subunit interface, positioned to interact with the gamma-phosphate of bound nucleoside 5' triphosphate. In this respect, it is analogous to arginine fingers found in other nucleotide-hydrolyzing enzymes. When Arg-522 is replaced with alanine (gp4-R522A) or lysine (gp4-R522K), the rate of dTTP hydrolysis is significantly decreased. dTTPase activity of the altered proteins is not inhibited by Vi, suggesting the loss of an interaction between Vi and gene 4 protein. gp4-R522A cannot unwind DNA, whereas gp4-R522K does so, proportionate to its dTTPase activity. However, gp4-R522K cannot stimulate T7 polymerase activity on double-stranded DNA. These findings support the involvement of the Arg-522 residue in the energy coupling mechanism.

Publication types

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

MeSH terms

  • Arginine*
  • Bacteriophage T7 / enzymology*
  • Base Sequence
  • Crystallography, X-Ray
  • DNA Primase / chemistry*
  • DNA Primase / metabolism*
  • Escherichia coli / virology
  • Kinetics
  • Models, Molecular
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Oligodeoxyribonucleotides
  • Protein Conformation
  • Recombinant Proteins / chemistry
  • Substrate Specificity
  • Thermodynamics
  • Thymine Nucleotides / metabolism


  • Oligodeoxyribonucleotides
  • Recombinant Proteins
  • Thymine Nucleotides
  • Arginine
  • DNA Primase
  • thymidine 5'-triphosphate