Translesion Synthesis Past the C8- and N²-Deoxyguanosine Adducts of the Dietary Mutagen 2-Amino-3-methylimidazo[4,5-f]quinoline in the NarI Recognition Sequence by Prokaryotic DNA Polymerases

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) is found in cooked meats and forms DNA adducts at the C8- and N²-positions of dGuo after appropriate activation. IQ is a potent inducer of frameshift mutations in bacteria and is carcinogenic in laboratory animals. We have incorporated both IQ-adducts into the G₁- and G₃-positions of the NarI recognition sequence (5‘-G₁G₂CG₃CC-3‘), which is a hotspot for arylamine modification. The in vitro replication of the oligonucleotides was examined with Escherichia coli pol I Klenow fragment exo^-, E. coli pol II exo^-, and Sulfolobus solfataricus P2 DNA polymerase IV (Dpo4), and the extension products were sequenced by tandem mass spectrometry. Replication of the C8-adduct at the G₃-position resulted in two-base deletions with all three polymerases, whereas error-free bypass and extension was observed at the G₁-position. The N²-adduct was bypassed and extended by all three polymerases when positioned at the G₁-position, and the error-free product was observed. The N²-adduct at the G₃-position was more blocking and was bypassed and extended only by Dpo4 to produce an error-free product. These results indicate that the replication of the IQ-adducts of dGuo is strongly influenced by the local sequence and the regioisomer of the adduct. These results also suggest a possible role for pol II and IV in the error-prone bypass of the C8-IQ-adduct leading to frameshift mutations in reiterated sequences, whereas noniterated sequences result in error-free bypass.