“…He points out, for example, that when no change in X-ray mutability was noted in excision-deficient mutants, it was explained that the mutagenic lesions were not subject to excision repair; on the other hand, a report of reduced mutability in excision-deficient strains following y-irradiation led to the explanation that mutagenesis was due to errors in excision repair; a third report linked a decrease in X-ray mutability to REG mutants and suggested that such mutability was the result of errors in recombinational repair. In suggesting that such explanations of opposing effects are suspect, Newcombe (1971) proposes that additional, less understood, systems may prove to be more directly related to radiation mutagenesis. The association between mutator effects and altered DNA poly merizing enzymes (Drake, 1969) suggests that continued research into the nature and role of DNA polymerase may well bear out Newcombe's prediction (Newcombe, 1971).…”