LEARNING ABOUT DNA-POLYMERASE FUNCTION BY STUDYING ANTIMUTATOR DNA-POLYMERASES

Mutant bacteriophage T4 DNA polymerases exist that appear primarily to reduce the frequency of AT-to-GC transitions when this 'antimutator' phenotype is assessed by genetic methods. This observation disagrees w ith in vitro studies, which indicate that T4 antimutator DNA polymeras es have increased proofreading abilities and effectively edit all type s of base substitution errors. One explanation that reconciles the app arent in vivo mutational specificity of antimutator DNA polymerases wi th their biochemical properties is that the in vivo mutational specifi city identifies mismatched primer-termini that are corrected less effi ciently by the wild-type level of proofreading activity, but are corre cted if proofreading is increased.