Rs. Tebbs et Lj. Romano, MUTAGENESIS AT A SITE-SPECIFICALLY MODIFIED NARI SEQUENCE BY ACETYLATED AND DEACETYLATED AMINOFLUORENE ADDUCTS, Biochemistry, 33(30), 1994, pp. 8998-9006
A hotspot for mutagenesis by N-acetyl-2-aminofluorene (AAF) was site-s
pecifically modified with 2-aminofluorene (AF) and AAF adducts, and th
e mutation frequencies and specificities were determined and compared.
Previous work has shown that the presence of an AAF adduct in a NarI
sequence (GGCGCC) results a high mutation frequency for a CG double ba
se pair deletion. In the present study, an M13 derivative was construc
ted that contained a NarI recognition sequence in the beta-galactosida
se gene of bacteriophage M13mp9. This derivative was site-specifically
modified with either an AF or an AAF adduct, the products were charac
terized, and these templates were then transformed into Escherichia co
li wild-type strain JM103 or uvrA strain SMH12. The levels and mutatio
n spectra were determined either with or without SOS induction. It was
found that, with SOS functions induced, the measured mutation frequen
cies were substantially higher in all cases. More importantly, the typ
es of mutations induced by the AAF and AF adducts were very different:
AAF adducts induced almost exclusively CG double base deletion mutati
ons, whereas AF adducts gave rise specifically to base-substitution mu
tations. The AF-derived mutation spectrum included both G to T and G t
o A mutations. The results are discussed in light of the current views
on the relationship between the DNA structure and mutagenesis.