Genetic analysis of the interaction between bacteriophage T7 DNA polymerase and Escherichia coli thioredoxin

Proc Natl Acad Sci U S A. 1992 Oct 15;89(20):9774-8. doi: 10.1073/pnas.89.20.9774.


Gene 5 protein of bacteriophage T7 is a nonprocessive DNA polymerase. During infection of Escherichia coli, T7 annexes the host protein thioredoxin for use as a processivity factor for T7 DNA polymerase. We describe here a genetic method to investigate the interaction between T7 gene 5 protein and E. coli thioredoxin. The strategy is to use thioredoxin mutants that are unable to support the growth of wild-type T7 phage to select for T7 revertant phage that suppress the defect in thioredoxin. A thioredoxin mutation that replaces glycine at position 74 with aspartic acid fails to support the growth of wild-type T7. This mutation is suppressed by six different mutations within T7 gene 5, each of which results in a single amino acid substitution within gene 5 protein. Three of the suppressor mutations are located within the putative polymerization domain of gene 5 protein, and three are located within the putative 3'-to-5' exonucleolytic domain. Each suppressor mutation alone is necessary and sufficient to confer the revertant phenotype.

Publication types

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

MeSH terms

  • DNA Replication
  • DNA-Directed DNA Polymerase / metabolism*
  • DNA-Directed DNA Polymerase / ultrastructure
  • Escherichia coli / metabolism
  • Genes, Suppressor
  • Genetic Complementation Test
  • Macromolecular Substances
  • Mutagenesis, Site-Directed
  • Mutation
  • Protein Structure, Tertiary
  • Structure-Activity Relationship
  • T-Phages / enzymology*
  • Thioredoxins / metabolism*
  • Viral Proteins / metabolism
  • Viral Proteins / ultrastructure


  • Macromolecular Substances
  • Viral Proteins
  • Thioredoxins
  • DNA-Directed DNA Polymerase