title: Carcinogen-induced frameshift mutagenesis in repetitive sequences.
abstract: We have constructed plasmids pS3G-1 and pSG4 that contain single acetylaminofluorene adducts within contiguous runs of three (5'-CCCG1G2G3-3') and four (5'-CG1GGG4T-3') guanine residues, respectively. In Escherichia coli, the frequency of induced -1 frameshift mutations was strongly dependent on the position of modification: pS3G-G3 was approximately 100-fold and 10-fold more mutagenic than pS3G-G1 and pS3G-G2, respectively; pSG4-G4 was approximately 600-fold more mutagenic than pSG4-G1. Mutagenesis was SOS-dependent and was markedly reduced in bacteria that were proficient in nucleotide excision repair as compared to a repair-deficient uvrA6 mutant. DNA sequencing showed that -1 frameshift events in pS3G-1 consisted of either targeted mutations (greater than 90% of induced mutations) within the guanine sequence or semitargeted mutations (greater than 10%) in the 5' flanking repetitive cytosine sequence. Semitargeted events, which were observed when acetylaminofluorene modification was at G1 and G2, show that a lesion can reduce the fidelity of replication at positions 5' to its location on the template strand. No semitargeted frameshifts were observed in plasmid pSG4, which lacks a repetitive sequence 5' to the adduct. Our results are consistent with a model for frameshift mutagenesis in which the acetylaminofluorene adduct (i) allows accurate incorporation of cytosine opposite the bulky lesion during DNA synthesis and (ii) impedes elongation of primer/template termini formed opposite the adduct or 5' to the adduct on the template strand, providing increased opportunity for the formation of slipped frameshift intermediates.
authors.affiliation: Groupe de Cancérogenèse et de Mutagenèse Moléculaire et Structurale, Institut de Biologie Moléculaire et Cellulaire du Centre National de la Recherche Scientifique, Strasbourg, France.
authors.forename: I B
authors.initials: IB
authors.lastname: Lambert
authors.forename: R L
authors.initials: RL
authors.lastname: Napolitano
authors.forename: R P
authors.initials: RP
authors.lastname: Fuchs
mesh_terms: D015073:2-Acetylaminofluorene / Q000737:chemistry / Q000494:pharmacology*; D001483:Base Sequence; D002273:Carcinogens / Q000494:pharmacology*; D004247:DNA / Q000737:chemistry; D004249:DNA Damage; D004260:DNA Repair; D016368:Frameshift Mutation; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010957:Plasmids; D012091:Repetitive Sequences, Nucleic Acid
chemical_list: D002273:Carcinogens; D004247:DNA; D015073:2-Acetylaminofluorene