A unique loop in T7 DNA polymerase mediates the binding of helicase-primase, DNA binding protein, and processivity factor

Proc Natl Acad Sci U S A. 2005 Apr 5;102(14):5096-101. doi: 10.1073/pnas.0501637102. Epub 2005 Mar 28.


Bacteriophage T7 DNA polymerase (gene 5 protein, gp5) interacts with its processivity factor, Escherichia coli thioredoxin, via a unique loop at the tip of the thumb subdomain. We find that this thioredoxin-binding domain is also the site of interaction of the phage-encoded helicase/primase (gp4) and ssDNA binding protein (gp2.5). Thioredoxin itself interacts only weakly with gp4 and gp2.5 but drastically enhances their binding to gp5. The acidic C termini of gp4 and gp2.5 are critical for this interaction in the absence of DNA. However, the C-terminal tail of gp4 is not required for binding to gp5 when the latter is bound to a primer/template. We propose that the thioredoxin-binding domain is a molecular switch that regulates the interaction of T7 DNA polymerase with other proteins of the replisome.

Publication types

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

MeSH terms

  • Bacteriophage T7 / enzymology
  • Bacteriophage T7 / genetics
  • Base Sequence
  • Binding Sites / genetics
  • DNA Primase / chemistry*
  • DNA Primase / genetics
  • DNA Primase / metabolism*
  • DNA, Viral / genetics
  • DNA-Binding Proteins / chemistry*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • DNA-Directed DNA Polymerase / chemistry*
  • DNA-Directed DNA Polymerase / genetics
  • DNA-Directed DNA Polymerase / metabolism*
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / metabolism
  • Genes, Viral
  • Models, Biological
  • Models, Molecular
  • Mutagenesis
  • Protein Conformation
  • Sequence Deletion
  • Sulfinic Acids
  • Thioredoxins / chemistry
  • Thioredoxins / metabolism
  • Viral Proteins / chemistry*
  • Viral Proteins / genetics
  • Viral Proteins / metabolism*


  • DNA, Viral
  • DNA-Binding Proteins
  • Escherichia coli Proteins
  • Sulfinic Acids
  • Viral Proteins
  • gene 2.5 protein, Enterobacteria phage T7
  • thiosulfinic acids
  • Thioredoxins
  • DNA Primase
  • bacteriophage T7 induced DNA polymerase
  • DNA-Directed DNA Polymerase