Biochemical basis of genotoxicity of heterocyclic arylamine food mutagens -: Human DNA polymerase η selectively produces a two-base deletion in copying the N2-guanyl adduct of 2-amino-3-methylimidazo[4,5-f] quinoline but not the C8 adduct at the NarI G3 site

Heterocyclic arylamines are highly mutagenic and cause tumors in animal models. The mutagenicity is attributed to the C-8- and N-2-G adducts, the latter of which accumulates due to slower repair. The C-8- and N-2-G adducts derived from 2-amino-3- methylimidazo[4,5-f] quinoline (IQ) were placed at the G(1) and G(3) sites of the NarI sequence, in which the G3 site is an established hot spot for frameshift mutation with the model arylamine derivative 2-acetylaminofluorene but G1 is not. Human DNA polymerase (pol) eta extended primers beyond template G-IQ adducts better than did pol kappa and much better than pol iota or delta. In 1-base incorporation studies, pol eta inserted C and A, pol iota inserted T, and pol kappa inserted G. Steady-state kinetic parameters were measured for these dNTPs opposite the C-8- and N-2-IQ adducts at both sites, being most favorable for pol eta. Mass spectrometry of pol eta extension products revealed a single major product in each of four cases; with the G(1) and G(3) C-8- IQ adducts, incorporation was largely error-free. With the G(3) N-2-IQ adduct, a - 2 deletion occurred at the site of the adduct. With the G(3) N-2-IQ adduct, the product was error-free at the site opposite the base and then stalled. Thus, the pol eta products yielded frame-shifts with the N-2 but not the C-8 IQ adducts. We show a role for pol eta and the complexity of different chemical adducts of IQ, DNA position, and DNA polymerases.