mutagenesis induced by 5bromouracil and methyl methane sulfonate role of dna polymerase i a pola1 mutation in the dna polymerase i gene of e coli results in a drastic reduction of the frequency of mutagenesis induced by 5bromo2deoxyuridine budr comparisons of the effect of a pola1 mutation on mutagenesis induced by methyl methane sulfonate mms ultraviolet irradiation uv and 2aminopurine 2ap demonstrated that a similar effect of a pola1 mutation is observed with mms this effect is much less marked with uvand2apinduced mutagenesis it follows that dna polymerase i plays a key role in the process of mutagenesis induced by bu and mms bearing in mind that mutagenesis provoked by uv mms and bu involves participation of the accompanying induced errorprone system the sources of the differences in requirement for dna polymerase i are critically examined