Induction of mutations by replication of malondialdehyde modified M13 DNA in Escherichia coil: determination of the extent of DNA modification, genetic requirements for mutagenesis, and types of mutations induced
The mutagenicity of the lipid peroxidatlon product, malondialdehyde (MDA), was measured in the lacZα forward mutation assay using a recombinant M13 phage, M13MB102. Single-stranded M13MB102 DNA was reacted with MDA at neutral pH and the modified DNA was transformed Into strains of Escherichia coil Induced for the SOS response. Increasing concentrations of MDA led to an increase In lacZα-mutations coincident with an Increase In the level of the major MDA-deoxyguanoslne adduct. Spontaneous and MDA-lnduced M13MB102 mutants were collected and the lacZα target region was subjected to automated DNA sequence analysis. The most common sequence changes induced by MDA were base-pair substitutions (76%). Of these, 43% (29/68) were transverslons, most of which were G→ (24/29). Transitions account for 57% of the base-pair substitutions (39/68) and were comprised exclusively of C→T (22/39) and A→ (17/39). Frameshlft mutations were identified In 16% of the induced mutants and were comprised of mainly single base additions occurring In runs of reiterated bases (11/14). The diversity of base-pair substitution and franieshift mutations induced by MDA at low levels of adduction suggests It may be an Important contributor to endogenous mutagenesls and carcinogenesis in aerobic organisms.