Induction of mutations by N-acetoxy-N-acetyl-2-aminofluorene modified M13 viral DNA.

The specificity of N-(deoxyguanosin-8-yl)-N-acetyl-2-aminofluorene (G-8-AAF) adducts in double-stranded DNAs from M13mp8 and M13mp9 bacteriophage was determined following transfection of modified DNA with multiple adducts into competent JM103 cells. Mutant phages were selected by phenotypic screening for colorless or light blue plaques indicating a defective beta-galactosidase marker enzyme. Mutation frequencies of phage DNA with G-8-AAF adducts were increased up to 8-fold in SOS-induced host cells as compared to the uninduced JM103 host cells. DNA sequencing of mutants from SOS-induced host cells indicated approximately 52% frameshifts and 39% base substitutions in M13mp8 DNA and 65% frameshifts and 25% base substitutions in M13mp9 DNA. Mutation spectra exhibited mutations at many sites within the bp 6200-6400 region; one mutational hotspot at position 6343-6347 (5' GGGGG 3') for frameshifts was also observed. The G-8-AAF adduct induced mostly single base deletions at this site. In contrast, a deacetylated adduct, N-(deoxyguanosin-8-yl)-2-aminofluorene (G-8-AF) in our previous experiments induced mostly single base additions at the same position indicating the ability of adduct structure to modulate the specificity of frameshift mutations. A number of other frameshift mutations (11 out of 29) were observed within non-repetitive and non-palindromic sequences. Molecular mechanisms for the induction of these mutations by DNA perturbations produced by the G-8-AAF adducts are discussed.