The major, N2-dG adduct of (+)-anti-B[a]PDE shows a dramatically different mutagenic specificity (predominantly, G --> A) in a 5'-CGT-3' sequence context.
Mutations induced by the (+)-anti diol epoxide of benzo[a]pyrene [(+)-anti-B[a]PDE] were described previously in the supF gene of the Escherichia coli plasmid pUB3 [Rodriguez et al.(1993) Biochemistry, 32, 1759]. (+)-anti-B[a]PDE induced a complex pattern of mutations, including insertions, deletions, frameshifts, as well as base substitution mutations, which for G:C base pairs alone included a significant fraction of G:C --> T:A, A:T and C:G mutations. A variety of results suggest that most of these mutations arise from the major adduct ([+ta]-B[a]P-N2-dG), raising the question how can a single adduct induce different kinds of mutations? Our working hypothesis in this regard is that (1) an adduct can adopt multiple conformations; (2) different conformations cause different mutations; and (3) adduct conformation is controlled by various factors, such as DNA sequence context. To investigate what conformation is associated with what mutation, it is essential to find examples where [+ta]-B[a]P-N2-dG induces principally one kind of mutation as a prelude to the study in that same context of the conformation(s) potentially relevant to mutagenesis. Earlier work indicated that (+)-anti-B[a]PDE gave a preponderance of G --> A mutations in a 5'-CGT-3 sequence context, and herein it is shown that these mutations are likely to be attributable to the major adduct, since in this same sequence context [+ta]-B[a]P-N2-dG studied site specifically also induces principally G --> A mutations ( approximately 82%). Previously, [+ta]-B[a]P-N2-dG was shown to induce principally G --> T mutations (approximately 97%) in a 5'-TGC-3' sequence context. Thus, by simply altering its surrounding sequence context this adduct can give a preponderance of either G --> A or G --> T mutations. This is the most dramatic change in base substitution mutagenic specificity for an adduct described to date and illustrates that the qualitative pattern of mutagenesis by a bulky adduct can be remarkably diverse.
Shukla
R
R
Department of Biology, Boston University, Boston, Massachusetts 02215, USA.
Liu
T
T
Geacintov
N E
NE
Loechler
E L
EL
D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D018736:DNA Adducts / Q000737:chemistry*; D016153:Genes, Suppressor; D016296:Mutagenesis; D009153:Mutagens / Q000737:chemistry*; D009154:Mutation; D010957:Plasmids; D012343:RNA, Transfer / Q000235:genetics
D018736:DNA Adducts; D009153:Mutagens; C043931:benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide-DNA; C096275:supF tRNA; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; D012343:RNA, Transfer