Response of repair-competent and repair-deficient Escherichia coli to three O6-substituted guanines and involvement of methyl-directed mismatch repair in the processing of O6-methylguanine residues.
Response of repair-competent and repair-deficient Escherichia coli to three O6-substituted guanines and involvement of methyl-directed mismatch repair in the processing of O6-methylguanine residues.
复制标题
具有修复能力和修复缺陷的大肠杆菌对三个 O6 取代鸟嘌呤的响应以及甲基定向错配修复参与 O6-甲基鸟嘌呤残基的加工。
DOI：
10.1021/bi00197a020
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发表时间：
1994
期刊：
影响因子：
2.9
通讯作者：
Moschel,RC
中科院分区：
文献类型：
--
作者：
Pauly,GT;Hughes,SH;Moschel,RC
在lacZ ′基因的ATG起始密码子内含有位点特异性掺入的06-甲基-（m6 G）、06-乙基-（e6 G）或06-苄基鸟嘌呤（b6 G）的质粒被用于转化大肠杆菌，所述大肠杆菌在大肠杆菌中的一种或两种中具有修复能力或缺陷。coliC 1-烷基鸟嘌呤-DNA烷基转移酶、uvr（ABC）切除修复系统、recvl介导的重组系统或甲基化指导的错配修复系统。对集落的内收物诱导突变进行表型评分。用含有e6 G或b6 G的质粒，加合物诱导突变的频率低，并且独立于转化菌株的修复能力。含有m6 G残基的质粒引起了类似的反应，但在所有的错配修复缺陷株。所有β-取代鸟嘌呤的致突变性通常较低，这被解释为反映了修饰链复制的加合物诱导停滞，而未修饰的互补链正常复制。对m6 G突变中错配修复参与的研究表明，m6 G：T碱基对比m6 G：C碱基对更容易加工，表明涉及m6 G残基的错配修复发生在复制后。这些数据支持了一个模型，其中E。大肠杆菌甲基化指导的错配修复系统转移含有前诱变m6 G的质粒：除了C^-烷基鸟嘌呤-DNA烷基转移酶修复和切除修复机制外，T碱基对进入复制停滞复合物提供了另一条防御C^-甲基鸟嘌呤致突变性的防线。质粒或病毒载体中的修饰碱基以及将这些载体引入细菌或哺乳动物细胞中可以提供关于生物系统如何响应的有价值的信息特定致癌物-DNA加合物（Basu & Essigmann，1988; Strauss & Loeb，1989）。已经使用这种方法检查了几种致癌物修饰的碱基的致突变效力（Singer
Revised Manuscript Received May 24, 1994* abstract: Plasmids containing a site-specifically incorporated 06-methyl-(m6G), C^-ethyl-(e6G), or O6-benzylguanine (b6G) within the ATG initiation codon of the lacZ'gene were used to transform Escherichia coli that were repair proficient or deficient in one or both of the E. coli C^-alkylguanine-DNA alkyltransferases, the uvr (ABC) excision repair system, the recvl-mediated recombination system, or the methylation-directed mismatch repair system. Colonies were scored phenotypically for adduct-induced mutations. With plasmids containing either e6G or b6G, the frequency of adduct-induced mutation was low and independent of the repair proficiency of the strain transformed. Plasmids containing an m6G residue elicited similar responses in all but the mismatch repair-deficient strain. The generally low mutagenicity of all the^-substituted guanines was interpreted as reflecting an adduct-induced arrest of replication of the modified strand while the unmodified complementary strand was replicated normally. Studies of the involvement of mismatch repair in m6G mutagenesis showed that m6G: T base pairs were more readily processed than m6G: C base pairs, indicatingthat mismatch repair involving m6G residues occurs after replication. These data support a model in which the E. coli methylation-directed mismatch repair system diverts plasmids containing promutagenic m6G: T base pairs into replication-arrested complexes providing another lineof defense against C^-methylguanine mutagenicity in addition to C^-alkylguanine-DNA alkyltransferase repair and excision repair mechanisms.Site-specific incorporation of carcinogen-modified bases in plasmid or viral vectors and introduction of these vectors into bacteria or mammalian cells can provide valuable information on how biological systems respond to particular carcinogen-DNA adducts (Basu & Essigmann, 1988; Strauss & Loeb, 1989). The mutagenic potencies of several carcinogenmodified bases have been examined using this approach (Singer