Mutagenic effects at hprt locus and in minisatellite sequences induced in V79 cells by treatments with UV and methyl-nitro-nitroso guanidine

DNA alterations induced in V79 cells treated with UV light or methyl-nitro-nitrosoguanidine were analyzed by the mutagenicity test at the hprt locus and by DNA fingerprint analysis. Treated and control cells were seeded in the presence or absence of 6-thioguanine to determine mutant frequency and cell survival. From clonal cultures of the same cell populations we isolated a number of clones and grew them up individually to obtain appropriate amounts of DNA. High molecular weight DNA was digested with HinfI or HaeIII and hybridized with ³²P-labelled 33.15 multilocus probe. The induction of 6-thioguanine resistant cells depended on the mutagen does. The highest value of mutant frequency obtained was 7475 × 10⁻⁶ (MNNG, 27μM), corresponding to 0.7 percent of clonable cells. DNA fingerprint analysis carried out on the same treated cells showed that DNA rearrangements occurred at minisatellites much more frequently than in transcribed sequences. UV irradiation produced the highest frequency of variation, modifying minisatellite patterns in about 50 percent of the analyzed clones.