Mutagenesis induced by 5-bromouracil 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 5-bromo-2'-deoxyuridine (BUdR). Comparisons of the effect of a polA1 mutation on mutagenesis induced by methyl methane sulfonate (MMS), ultraviolet irradiation (UV) and 2-aminopurine (2-AP) demonstrated that a similar effect of a polA1 mutation is observed with MMS. This effect is much less marked with UV-and-2-AP-induced 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 error-prone system, the sources of the differences in requirement for DNA polymerase I are critically examined.