Analysis of forward mutations induced by N-methyl-N'-nitro-N-nitrosoguanidine in the bacteriophage P22 mnt repressor gene

UMMS Affiliation

Department of Biochemistry and Molecular Pharmacology

Publication Date


Document Type



Base Sequence; DNA, Viral; *Genes, Viral; Methylnitronitrosoguanidine; *Mutation; Plasmids; Repressor Proteins; Salmonella Phages; Transcription Factors


Bacteria | Biochemistry, Biophysics, and Structural Biology | Genetic Phenomena | Pharmacology, Toxicology and Environmental Health


We describe the isolation and genetic characterization of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced mutations in the phage P22 mnt repressor gene cloned in plasmid pBR322. Mutations in the mnt repressor gene or its operator on this plasmid, pPY98, confer a tetracycline resistance phenotype, whereas the wild-type plasmid confers tetracycline sensitivity. Cells carrying pPY98 were briefly exposed to MNNG to give 20 to 40% survival and a 50- to 100-fold increase in tetracycline-resistant cells. DNA sequence analysis showed that 29 of 30 MNNG-induced mutations were GC-to-AT transitions and one was an AT-to-GC transition. About 80% of the mutations are in three hotspots. This mutation spectrum is consistent with the proposed mechanism of mutagenic action of MNNG, which involves mispairing of an alkylated base, O6-methylguanine. The mnt gene may be a useful target for determining mutagenic specificity at the nucleotide level because forward mutations are easily isolated, the target size is small, and the DNA sequence changes of mutations can be determined rapidly.

DOI of Published Version



J Bacteriol. 1986 Apr;166(1):34-7.

Journal/Book/Conference Title

Journal of bacteriology

Related Resources

Link to Article in PubMed

PubMed ID