Locations of amino acid substitutions in bacteriophage T4 tsL56 DNA polymerase predict an N-terminal exonuclease domain.

J Virol (1989), Volume 63, Page 4762


The amino acid substitutions responsible for the temperature-sensitive (ts) and mutator phenotypes of the classical bacteriophage T4 DNA polymerase mutant tsL56 were determined. tsL56 DNA polymerase has two mutations in the 5' end of the DNA polymerase gene (g43) that produce two amino acid substitutions: codon 89, alanine to threonine, and codon 363, aspartate to asparagine. Both mutations are required for the strong ts and mutator phenotypes. The increased error rate of the tsL56 DNA polymerase is due to a reduction in 3'----5' exonuclease activity relative to polymerase activity (N. Muzyczka, R. L. Poland, and M. J. Bessman, J. Biol. Chem. 247:7116-7122, 1972). Thus, the locations of the tsL56 mutations suggest that the 3'----5' exonuclease domain resides in the N-terminal region. Several other ts DNA polymerase mutant strains isolated with tsL56 also have mutator or antimutator phenotypes. The nucleotide changes in these important mutant strains were also determined. This mutant collection, combined with collections of g43 amber mutants and mutants selected on the basis of a strong mutator phenotype (L. J. Reha-Krantz, J. Mol. Biol. 202:711-724, 1988), contains nearly 70 different DNA polymerase mutations. The numerous T4 DNA polymerase mutations are valuable for DNA polymerase structure-function and fidelity studies.



Exonuclease Activity, Fidelity, Mutational Analysis, Structure and Structure/Function


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Polymerase Reference Property Result Context
T4 A89TD363N Reha-Krantz LJ1989 Nucleotide Substitution Rate 20 Mutation frequency (relative to WT) Technique: ac forward mutational assay
T4 D363N Reha-Krantz LJ1989 Nucleotide Substitution Rate 5 Mutation frequency (relative to WT) Technique: ac forward mutational assay
T4 A89T Reha-Krantz LJ1989 Nucleotide Substitution Rate 8 Mutation frequency (relative to WT) Technique: ac forward mutational assay

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