Construction of plasmids containing a unique acetylaminofluorene adduct located within a mutation hot spot. A new probe for frameshift mutagenesis

N-2-acetylaminofluorene (AAF), a potent rat liver carcinogen, binds primarily to the C-8 position of guanine residues. In a bacterial forward mutation assay, more than 90% of the mutations induced by -AAF adducts are frameshift mutations located at specific sites: the so-called mutation hot spots. We are particularly interested in a class of -2 frameshift mutations occurring within a specific sequence, the NarI sequence. The NarI site, GGCGCC, contains three guanine residues that are approximately equally reactive toward -AAF substitution. To study further the mechanism by which mutations are induced by -AAF adducts at this site, we designed a new plasmid probe. In this paper we describe the construction and the effectiveness of this probe, pSM14, which provides a simple phenotypic test for detecting frameshift mutations within the NarI site. The construction and the characterization of plasmids with a single -AAF adduct in each of the three positions of the NarI site are also described. The strategy of construction that was used involves the ligation of oligonucleotides containing a single adduct in a NarI site into a gapped-duplex pSM14 plasmid. Plasmids that have successfully integrated the oligonucleotides by ligation at both the 5' and the 3' ends were purified by centrifugation on CsCl gradients. These constructs have been used in single adduct mutation studies.