Shukla R, Liu T, Geacintov N E, Loechler E L
Department of Biology, Boston University, Boston, Massachusetts 02215, USA.
Biochemistry. 1997 Aug 19;36(33):10256-61. doi: 10.1021/bi970541+.
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.
苯并[a]芘的(+)-反式二醇环氧化物[(+)-反式-B[a]PDE]诱导的突变先前已在大肠杆菌质粒pUB3的supF基因中有所描述[罗德里格斯等人(1993年)《生物化学》，32卷，1759页]。(+)-反式-B[a]PDE诱导了一种复杂的突变模式，包括插入、缺失、移码以及碱基替换突变，仅对于G:C碱基对而言，其中很大一部分是G:C→T:A、A:T和C:G突变。各种结果表明，这些突变大多源于主要加合物([+ta]-B[a]P-N2-dG)，这就引出了一个问题：单一加合物如何能诱导不同类型的突变？我们在这方面的工作假设是：(1) 一种加合物可以采取多种构象；(2) 不同的构象导致不同的突变；(3) 加合物构象受各种因素控制，如DNA序列背景。为了研究哪种构象与哪种突变相关，找到[+ta]-B[a]P-N2-dG主要诱导一种突变的例子至关重要，以此作为在同一背景下研究可能与诱变相关的构象的前奏。早期工作表明，在5'-CGT-3'序列背景下，(+)-反式-B[a]PDE产生的G→A突变占优势，本文表明这些突变可能归因于主要加合物，因为在相同的序列背景下，位点特异性研究的[+ta]-B[a]P-N2-dG也主要诱导G→A突变(约82%)。此前，[+ta]-B[a]P-N2-dG在5'-TGC-3'序列背景下主要诱导G→T突变(约97%)。因此，仅通过改变其周围的序列背景，这种加合物就能产生G→A或G→T突变中的一种占优势的情况。这是迄今为止所描述的加合物碱基替换诱变特异性最显著的变化，说明大体积加合物诱变的定性模式可能非常多样。
