MUTATION SPECTRUM OF 4-NITROQUINOLINE 1-OXIDE-DAMAGED SINGLE-STRANDEDSHUTTLE VECTOR DNA TRANSFECTED INTO MONKEY CELLS

4-Nitroquinoline 1-oxide (4NQO) is a potent mutagen and carcinogen whi ch induces two main guanine adducts at positions C8 and N2. We recentl y determined the mutation spectrum induced by the ultimate metabolite of 4NQO, acetoxy-4-aminoquinoline 1-oxide in the M13lacZ'/E. coli lacZ Delta M15 alpha-complementation assay. Our data suggested that dGuo-C 8-AQO induces (per se or via AP sites) G to Pyr transversions. Here we report our study on 4NQO mutagenesis in monkey cells. 4NQO lesions we re induced in vitro on a single-stranded (ss) DNA shuttle vector carry ing the supF tRNA gene. This vector was able to replicate both in mamm alian cells and in bacteria. The mutations induced in monkey cells wer e screened by the white/blue beta-galactosidase activity assay in E. c oli. We took advantage of the peculiar feature of ss supF DNA in which the extent of secondary structure may be a function of the temperatur e, with the dependence of the 4NQO-specific adduct spectrum on DNA sec ondary structure. We reasoned that mutational spectra derived from dam age induced in the presence (20 degrees C) or absence (70 degrees C) o f DNA secondary structure should be different. The result of sequencin g a total of 89 induced and spontaneous mutants confirmed that the spe ctra are statistically different. These data suggest that the two 4NQO guanine adducts may induce different mutations.