Involvement of DNA lesions and SOS functions in 5-bromouracil-induced mutagenesis.

Mutagenesis resulting from incorporation of 5-bromouracil (BU) in the DNA of E. coli K12 proceeds largely (approximately 80%) via misrepair of the lesions resulting from incorporation of the analogue. The premutational lesions are due principally to dehalogenation of incorporated BU residues, leading to formation of uracil residues, and removal of these by uracil-DNA glycosylase with formation of apyrimidinic sites. In the xthA mutant, defective in AP endonuclease, there is a several-fold increase in the frequency of BU-induced mutations, underlining the importance of AP sites in BU-induced mutagenesis. Premutational lesions undergo mutation frequency decline (MFD), which is subject to delay in the xthA mutant, pointing to some role of AP endonuclease in MFD, and further supporting involvement of AP sites in BU-induced mutagenesis. Efficient BU mutagenesis is dependent on the functions of the genes recA and umuC and non-mutated lexA protein.