[Induced mutagenesis of plasmid as well as chromosomal genes inserted into plasmid DNA. II. The mutagenic action of chemical factors].

To proceed the works on induced mutagenesis in plasmids, mutagenic effects of chemicals on the DNA of RSF2124 plasmid mediating colicine E1 biosynthesis and resistance to ampicillin, were studied. After exposure to mutagens, plasmid DNA was used to transform Escherichia coli C600 rk-mk-cells. The lethal effect was estimated from inactivation of the ampicillin marker, the mutagenic effect being measured by the appearance of mutants unable to synthesize colicine (Col-). The reaction of the plasmid DNA with a mutagen was stopped by 10-fold dilutions of aliquots in TEN buffer, followed by dialysis in 10 mH CaCl2 for 24 h. To select the most efficient mutagens for plasmid DNA, the compounds were predominantly tested which are known to be effective in other systems (transforming and transfecting DNA, microbial viruses). An a result, all chemicals tested by their activity were classified into 4 groups: inducing more than 100 fold increase (hydroxylamine, O-methylhydroxylamine); inducing 10 fold increase (UV-irradiation, lambda = 254 nm; W-mutagenesis, gamma-irradiation, nitrous acid, mitomycin C); inducing less than 10fold increase (indirect UV-mutagenesis, nitrous acid, beta-chloroethyldiethylamine hydrochloride, nitrosoguanidine); no mutagenic effect (acridine orange, ethyl methane sulfonate, sodium azide, O-beta-diethylhydroxylamine).