FPG PROTEIN PROTECTS ESCHERICHIA-COLI K-12 FROM MUTATION-INDUCTION BYTHE CARCINOGEN 4-NITROQUINOLINE 1-OXIDE

This paper investigates the role of the fpg gene product in protecting Escherichia coil cells against the lethal and mutagenic effects of 4- nitroquinoline 1-oxide (4NQO). To this end, the araD81 mutation which make the cells sensitive to L-arabinose was combined with an fpg-1::Kn (r) allele, in either an uvrA(+) or uvrA(-), umuC(+) or umuC(-), genet ic background. Mutation induction was monitored by selecting forward m utations to L-arabinose resistance (Ara(r)). The formamidopyrimidine-D NA glycosylase (Fpg protein) protected bacteria from 4NQO-induced muta genesis since Fpg(-) defective cells showed greater Ara(r) mutation in duction than fpg(+) bacteria did. This was confirmed since the increas ed sensitivity of the fpg(-) cells to mutagenesis by 4NQO was suppress ed when the Fpg protein was overproduced by placing the fpg gene in a multicopy plasmid vector. The fpg(-) mutation had no detectable influe nce on 4NQO mutagenesis in a uvrA(-) genetic background, but its effec t was magnified in umuC(-) cells. No influence on cell survival was ob served after 4NQO treatment. Our data suggest that 8-hydroxyguanine, a non-lethal, non-bulky and directly miscoding lesion, might be respons ible for the detected influence of Fpg protein expression on mutation induction by 4NQO. This is in agreement with the reported in vivo form ation of 8-hydroxyguanine in cellular DNA after 4NQO exposure. The inc reased 4NQO-induction of GC to TA transversions on fpg(-) bacteria fur ther support such a possibility. This work reinforces the role of Fpg protein in the bacterial defense against the mutagenicity by genotoxic agents.