title: Site-specific mutagenesis in vivo by single methylated or deaminated purine bases.
abstract: The technique of site-directed mutagenesis has been used to investigate the mutagenicity of O6-methylguanine (O6-MeG) or hypoxanthine introduced as a single lesion at a specific locus in an M13mp9 RF molecule constructed in vitro. Following transformation of O6-MeG-containing RF molecules into E. coli JM101, mutant progeny phage were produced at a frequency not significantly different from that observed with wild-type M13mp9 RF. The mutant yield was greatly enhanced by exhausting cellular O6-MeG DNA-methyltransferase before transformation. In contrast, hypoxanthine exhibited miscoding mutagenesis in the absence of interference with cellular repair mechanisms. This indicates that cellular hypoxanthine-DNA glycosylase acts inefficiently in the removal of hypoxanthine from DNA in vivo. The precise mutational changes induced by hypoxanthine were determined by DNA sequence analysis.
mesh_terms: D001483:Base Sequence; D003090:Coliphages / Q000235:genetics; D004260:DNA Repair; D004261:DNA Replication; D004279:DNA, Viral / Q000235:genetics; D006147:Guanine / Q000031:analogs & derivatives*; D019271:Hypoxanthine; D007042:Hypoxanthines; D008769:Methylnitronitrosoguanidine; D008780:Methyltransferases / Q000235:genetics; D009154:Mutation; D019853:O(6)-Methylguanine-DNA Methyltransferase
chemical_list: D004279:DNA, Viral; D007042:Hypoxanthines; D008769:Methylnitronitrosoguanidine; D019271:Hypoxanthine; D006147:Guanine; C008449:O-(6)-methylguanine; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase