Mutagenesis by (+)-anti-B[α]P-N2-Gua, the major adduct of activated benzo[α]pyrene, when studied in an Escherichia coli plasmid using site-directed methods

Abstract

The suspected major mutagenic adduct of benzo[α]pyrene, (+)-anti-B[α]P-N²-Gua, is built into the unique PstI recognition site of the Escherichia coli plasmid, pUC19, in order to study its mutagenic potential. The adduct can either be at G₄₃₇, which is replicated during leading strand DNA synthesis, or at G₄₃₈, which is replicated during lagging strand DNA synthesis. The DNA strand complementary to the strand containing the (+)-anti-B[α]P-N²-Gua adduct is saturated with UV lesions to minimize its potential to generate progeny. Although all in-frame mutations could have been detected, a G₄₃₇ → T transversion mutation is virtually exclusively obtained at a frequency of ˜0.04% per adduct following transformation into Uvr⁺E.coli when SOS is not induced, and ˜0.18% when SOS is induced. The mutation frequency of the adduct in a Uvr− backgraund is estimated to be ˜0.2% when SOS is not induced, and ˜0.9% when SOS is induced. The absence of G₄₃₈ → T mutations is rationalized. G → T mutations from (+)-anti-B[α]P-N²-Gua are compared to the mutational specificity of the ultimate mutagenic form of activated benzo[α]pyrene.