Dynamics of bacteriophage T4 DNA polymerase function: identification of amino acid residues that affect switching between polymerase and 3' --> 5' exonuclease activities

J Mol Biol. 1995 Nov 17;254(1):15-28. doi: 10.1006/jmbi.1995.0595.


Many DNA polymerases are multifunctional with the ability to replicate DNA as well as to proofread misincorporated nucleotides. Since polymerase and 3'--> 5' exonuclease activities appear to reside in spatially distinct active centers, there must be some mechanism for coordinating replication with proofreading and for transferring DNA between the two active centers. We have designed a genetic selection scheme to isolate bacteriophage T4 mutant DNA polymerases that are defective in "switching" between polymerase and exonuclease activities. Amino acid residues that affected active-site-switching were identified in four regions of the T4 DNA polymerase: two regions in the proposed exonuclease domain. Representative mutant DNA polymerases from each region were purified for biochemical studies. We propose that amino acid substitutions identified by mutational analysis affect critical contacts between T4 DNA polymerase and DNA that are required for transfer of DNA between the polymerase and exonuclease active centers.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acids / chemistry*
  • Base Sequence
  • Binding Sites
  • DNA Primers
  • DNA, Bacterial / metabolism*
  • DNA, Circular / metabolism
  • DNA, Single-Stranded / metabolism*
  • DNA-Directed DNA Polymerase*
  • Deoxyribonucleotides / metabolism
  • Exodeoxyribonuclease V
  • Exodeoxyribonucleases / chemistry
  • Exodeoxyribonucleases / metabolism*
  • Molecular Sequence Data
  • Mutation
  • Protein Conformation
  • Structure-Activity Relationship
  • Suppression, Genetic
  • Templates, Genetic
  • Viral Proteins / chemistry
  • Viral Proteins / metabolism*


  • Amino Acids
  • DNA Primers
  • DNA, Bacterial
  • DNA, Circular
  • DNA, Single-Stranded
  • Deoxyribonucleotides
  • Viral Proteins
  • gene 43 protein, Enterobacteria phage T4
  • DNA-Directed DNA Polymerase
  • Exodeoxyribonucleases
  • Exodeoxyribonuclease V