DNA binding by [2,5-14C]N-nitrosopyrrolidine in excision-repair proficient and deficient strains of Salmonella. Evidence for a major premutagenic adduct.

Little is known about the nature and possible genotoxic effects of the DNA adducts formed by N-nitrosopyrrolidine (NPYR) in whole animals. DNA binding in DNA isolated from [2,5-14C]NPYR-treated Salmonella was studied and attempts were made to monitor DNA adducts and correlate DNA binding with mutagenesis. NPYR was metabolized by hamster liver S-9 fraction in the presence of S.typhimurium TA1535 (uvrB-) or TA1975(uvrB+). DNA isolated from TA1535 contained about three times as much radioactivity as that isolated from TA1975, and NPYR-induced mutagenesis was several-fold higher in TA1535. The fraction of radioactivity incorporated into TA1535 was approximately 10(-5). Thermal hydrolysis of the 14C-containing DNA at neutral pH, followed by precipitation, released approximately 2/3 of the radioactivity into the supernatant. HPLC analysis of the supernatant revealed one major peak. This peak was absent in DNA from TA1975. Acid hydrolysis of the DNA precipitate after neutral hydrolysis released most of the residual radioactivity. Several small peaks were observed after HPLC analysis of the TA1535 acid hydrolysate or the TA1975 acid hydrolysate. These results demonstrate that NPYR is capable of binding to Salmonella DNA yielding one major product after hydrolysis and this DNA binding product appears to be repaired by the excision repair system. The fact that the major peak of radioactivity released from Salmonella is only found in the strain which is efficiently reverted by NPYR suggests that mutagenesis is dependent on the DNA modification leading to this peak.