Specificity of base substitution mutations induced by the dietary carcinogens 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhlP) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in Salmonella.

ABSTRACT

The base pair substitution mutational profiles induced by the heterocyclic amine cooked food mutagens PhlP and IQ in Salmonella typhimurium strains TA100 and TA1535 were determined by colony hybridization analysis. Both PhlP and IQ induced predominantly GC-->TA transversions in strain TA100 (rfa,delta uvrB/pKM101) with a pronounced preference for the second codon position (CCC--> CAC; 72% of total). PhlP also reverted strain TA1535 (rfa, delta uvrB) efficiently at concentrations similar to those required for strain TA100. In contrast to the PhlP-induced mutational profile observed in strain TA100, in strain TA1535 PhlP induced exclusively GC-->AT transitions at the second codon position (CCC-->CTC; 96-99% of total). Base substitution mutagenesis induced by heterocyclic amines related to PhlP is generally SOS-dependent, requiring the presence of plasmid pKM101 in Salmonella hisG46 strains. Thus, the SOS dependent reversion of S. typhimurium strain TA100 probably reflects error-prone lesion bypass at the major PhlP- guanosine adduct at the C-8 position. The GC-->AT transition mutations induced by PhlP in strain TA1535 appear to be SOS-independent, however, suggesting that these mutations may arise from the formation of PhlP-DNA adducts other than the replication-blocking C8-dG lesion.