MUTAGENIC SPECIFICITY OF THE FOOD MUTAGEN 2-AMINO-3-METHYLIMIDAZO[4,5-F]QUINOLINE IN ESCHERICHIA-COLI USING THE YEAST URA3 GENE AS A TARGET

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ), a strong mutagen/carcino gen, belongs to a group of heterocyclic amines that are formed (ng/g a mounts) during the cooking of protein containing food, The mutational specificity of IQ in Escherichia coli was determined in a forward muta tion assay using the yeast URA3 gene as a target. The plasmid pTU-AC, containing the target URA3, was randomly modified in vitro using N-hyd roxy-IQ, and subsequently transformed into an E.coli pyrF strain (DB66 56), Mutant clones were directly selected by their ability to grow on medium containing 5-fluoro-orotic acid,which is toxic to URA(3+) clone s and thereby selects for URA3(-) mutants. Single Strand Conformation Polymorphism (SSCP) was used to map the mutation-containing regions of URA3, so that it was necessary to sequence only the relevant, mutatio n-containing fragment and not the entire gene, At a modification level of 7 IQ-lesions/URA3 gene, the predominant mutations were base substi tutions (similar to 70%), followed by complex gene rearrangements (sim ilar to 20%) and frameshifts (similar to 10%). More than 96% of the ba se substitutions occurred at G:C base pairs and were predominantly G:C -->A:T transitions, followed by G:C-->T:A and G:C-->C:G transversions, Next neighbour analysis revealed that deoxyguanosines situated within the sequence 5'-TGC were more susceptible to mutations induced by IQ. With one exception, all frameshift mutations were -1 deletions at run s of three consecutive dGs, At higher IQ-modification levels, predomin antly complex sequence rearrangements were observed.