Mutation enhancing effect of o-vanillin in the lacZ gene of Escherichia coli: characterization of mutational spectrum

Abstract

The enhancing effect of o-vanillin (2-hydroxy-3-methoxybenz-aldehyde) on mutations induced by N-methyl- N′-nitro- N-nitrosoguanidine (MNNG) was characterized with mutational specificity. The mutational spectrum of MNNG-induced mutations in the presence of o-vanillin was compared with that in the absence of o-vanillin by means of a series of mutant lacZ genes in E. coli that can detect each of the six types of base substitutions and five kinds of frameshift events. In the absence of o-vanillin, the mutational spectrum induced by MNNG consisted mainly of G · C → A · T transitions and, to a lesser extent, −1(G · C) frameshift mutations. By adding o-vanillin at 75 μg/plate, a marked enhancement was observed in two transitions, G · C → A · T and A · T → G · C, and in two frameshift mutations, t-1(G · C) and −1(G · C). Only a small change was observed in the −2(C · G-G · C) fraction. Regarding the MNNG-induced frameshifts at the A · T base pair, the +1(A · T) frameshift was much more enhanced by o-vanillin than the −1(A · T) frameshift.