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-n itro-nitrosoguanidine were analyzed by the mutagenicity test at the hp rt locus and by DNA fingerprint analysis. Treated and control cells we re seeded in the presence or absence of 6-thioguanine to determine mut ant frequency and cell survival. From clonal cultures of the same cell populations we isolated a number of clones and grew them up individua lly to obtain appropriate amounts of DNA. High molecular weight DNA wa s digested with HinfI or HaeIII and hybridized with P-32-labelled 33.1 5 multilocus probe. The induction of 6-thioguanine resistant cells dep ended on the mutagen dose. The highest value of mutant frequency obtai ned was 7475 x 10(-6) (MNNG, 27 mu M), corresponding to 0.7 percent of clonable cells. DNA fingerprint analysis carried out on the same trea ted cells showed that DNA rearrangements occurred at minisatellites mu ch more frequently than in transcribed sequences. UV irradiation produ ced the highest frequency of variation, modifying minisatellite patter ns in about 50 percent of the analyzed clones.