ANALYSIS OF MUTATIONS INDUCED BY 2-AMINO-1-METHYL-6-PHENYLIMIDAZO[4,5-B]PYRIDINE (PHIP) IN HUMAN LYMPHOBLASTOID-CELLS

2-Amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP), a heterocycli c aromatic amine that is formed in abundance in cooked meats, has been found to be mutagenic in human lymphoblastoid TK6 cells at the thymid ine kinase and hypoxanthine-guanine phosphoribosyl transferase (hgprt) loci, The mutations induced at the hgprt locus have been analysed, Of the mutations that have been identified, 60% were found in the coding sequence of the gene, Forty percent were in the introns which resulte d in aberrant splicing and consequently, leading to exon losses in the mature hprt mRNA. Mutations resulting in a loss of exonIII appeared m ost frequently followed by losses of exonVI, exonVIII and partial loss of exonIX. All identified mutations occurred at GC base pairs, consis tent with the adducts of PhIP that have been found previously and sugg esting that the )-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, (dG -C8-PhIP) adduct may be the premutagenic lesion, Most of the mutations are GC-->TA transversions except for a cluster of single base pair de letions in a run of guanines. There appears to be strand bias in the i nduction of mutations with 85% of the mutations on the non-transcribed strand, Although the number of mutations analysed is limited (54 muta nts), there are several sites (positions 166 and 207 of the coding seq uence, and the splice acceptor site of exonIII) which are overrepresen ted, There is a preference for a 5'purine but not a strong bias for 3' A as has been found for other mutagens that form a premutagenic lesion at G. Triplet analysis shows that the triplets, 5'GGA3' and 5'AGG3', where the middle base is mutated are preferred.