INDUCTION OF MUTATIONS BY REPLICATION OF MALONDIALDEHYDE-MODIFIED M13DNA IN ESCHERICHIA-COLI - DETERMINATION OF THE EXTENT OF DNA MODIFICATION, GENETIC REQUIREMENTS FOR MUTAGENESIS, AND TYPES OF MUTATIONS INDUCED

The mutagenicity of the lipid peroxidation product, malondialdehyde (M DA), was measured in the lacZ(alpha) forward mutation assay using a re combinant M13 phage, M13MB102. Single-stranded M13MB102 DNA was reacte d with MDA at neutral pH and the modified DNA was transformed into str ains of Escherichia coli induced for the SOS response. Increasing conc entrations of MDA led to an increase in lacZ(alpha)-mutations coincide nt with an increase in the level of the major MDA-deoxyguanosine adduc t. Spontaneous and MDA-induced M13MB102 mutants were collected and the lacZ(alpha) target region was subjected to automated DNA sequence ana lysis. The most common sequence changes induced by MDA were base-pair substitutions (76%). Of these, 43% (29/68) were transversions, most of which were G-->T (24/29). Transitions account for 57% of the base-pai r substitutions (39/68) and were comprised exclusively of C-->T (22/39 ) and A-->G (17/39). Frameshift mutations were identified in 16% of th e induced mutants and were comprised of mainly single base additions o ccurring in runs of reiterated bases (11/14). The diversity of base-pa ir substitution and frameshift mutations induced by MDA at low levels of adduction suggests it may be an important contributor to endogenous mutagenesis and carcinogenesis in aerobic organisms.