Title: Extrachromosomal probes for mutagenesis by carcinogens: studies on the mutagenic activity of O6-methylguanine built into a unique site in a viral genome.

Authors: Essigmann, J M; Fowler, K W; Green, C L; Loechler, E L

Published In Environ Health Perspect, (1985 Oct)

Abstract: This work examines the mutagenic activity of O6-methylguanine (O6MeGua), a DNA adduct formed by certain carcinogenic alkylating agents. A tetranucleotide, 5'-HOTpm6GpCpA-3', was synthesized and ligated into a four-base gap in the unique Pst I site of the duplex genome of the E. coli virus, M13mp8. The double-stranded ligation product was converted to single-stranded form and used to transform E. coli to produce progeny phage. The mutation frequency of O6MeGua was defined as the percentage of progeny phage with mutations in their Pst I site, and this value was determined to be 0.4%. To determine the impact of DNA repair on mutagenesis, cellular levels of O6MeGua-DNA methyltransferase (an O6MeGua-repair protein) were depleted by treatment of host cells for virus replication with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) prior to viral DNA uptake. In these host cells, the mutation frequency due to O6MeGua increased markedly with increasing MNNG dose (the highest mutation frequency observed was 20%). DNA sequence analysis of mutant genomes revealed that in both MNNG treated and untreated cells, O6MeGua induced exclusively G to A transitions.

PubMed ID: 3910417

MeSH Terms: Base Sequence; Carcinogens/toxicity*; Coliphages/drug effects; Coliphages/genetics*; DNA Repair; Escherichia coli/drug effects; Escherichia coli/genetics*; Genes, Viral/drug effects*; Guanine/analogs & derivatives*; Guanine/analysis; Guanine/toxicity; Mutagens*; Mutation*; Oligodeoxyribonucleotides/chemical synthesis