INVIVO EVIDENCE THAT UV-INDUCED C-]T MUTATIONS AT DIPYRIMIDINE SITES COULD RESULT FROM THE REPLICATIVE BYPASS OF CIS-SYN CYCLOBUTANE DIMERS OR THEIR DEAMINATION PRODUCTS
INVIVO EVIDENCE THAT UV-INDUCED C-]T MUTATIONS AT DIPYRIMIDINE SITES COULD RESULT FROM THE REPLICATIVE BYPASS OF CIS-SYN CYCLOBUTANE DIMERS OR THEIR DEAMINATION PRODUCTS
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DOI：
10.1021/bi00053a011
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发表时间：
1993-01-19
期刊：
影响因子：
2.9
通讯作者：
TAYLOR, JS
中科院分区：
文献类型：
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作者：
JIANG, N;TAYLOR, JS
由UV光诱导的主要突变是在二嘧啶处的C -> T转变，并且由与二嘧啶光产物的C相对的A的掺入引起。A的掺入最常被解释为聚合酶的已知偏好，以对抗非指令性DNA损伤，如脱碱基位点（A规则）。然而，也有一些机制认为顺式-顺式二嘧啶光二聚体是指导性的。在一种这样的机制（互变异构体旁路）中，A的掺入由二聚体的C的互变异构体指导，所述C在碱基配对性质上与U等同[Person等人（1974）Genetics 78，1035-1049]。在另一种机制（脱氨基旁路）中，A的掺入由二聚体的U指导，所述U由二聚体的C的脱氨基产生[Taylor & O ′ Day（1990）Biochemistry 29，1624-1632]。这些机制的可行性进行了测试，通过获得一个TU二聚体在大肠杆菌中的突变谱，通过应用定点诱变的标准方法。为此，通过连接含有二聚体的十聚体构建含有位点特异性TU二聚体的41-mer，所述十聚体通过三联体敏化照射产生并用于在含有与二聚体相对的双错配的M13克隆的含尿嘧啶（+）链上引发DNA合成。该反应混合物用于检测尿嘧啶糖基化酶活性、光产物修复缺陷型E.大肠杆菌宿主，并对所有与亲本（+）或（-）链弱杂交的子代噬菌体进行测序。在非SOS条件下，TU二聚体几乎完全阻断复制，而在SOS条件下，它指导的掺入两个作为具有更高的特异性（96%）比将脱碱基位点。这些结果的紫外线诱导的TC -> TT突变的机制，并通过扩展到CT -> TT，CC -> TC，CC -> CT，和串联CC -> TT突变的影响，进行了讨论。
The major mutations induced by UV light are C --> T transitions at dipyrimidines and arise from the incorporation of A opposite the C of dipyrimidine photoproducts. The incorporation of A has most often been explained by the known preference of a polymerase to do so opposite noninstructional DNA damage such as an abasic site (A rule). There are also mechanisms that suppose, however, that cis-syn dipyrimidine photodimers are instructional. In one such mechanism (tautomer bypass), the incorporation of A is directed by the tautomer of a C of a dimer that is equivalent in base-pairing properties to U [Person et al. (1974) Genetics 78, 1035-1049]. In another mechanism (deamination bypass), the incorporation of A is directed by a U of a dimer that results from the deamination of the C of a dimer [Taylor & O'Day (1990) Biochemistry 29, 1624-1632]. The viability of these mechanisms was tested by obtaining the mutation spectrum of a TU dimer in Escherichia coli by application of a standard method for site-directed mutagenesis. To this end, a 41-mer containing a site-specific TU dimer was constructed via ligation of a dimer-containing decamer that was produced by triplet-sensitized irradiation and used to prime DNA synthesis on a uracil-containing (+) strand of an M13 clone containing a double mismatch opposite the dimer. The reaction mixture was used to transfect a uracil glycosylase proficient, photoproduct repair deficient E. coli host, and all progeny phage weakly hybridizing to the parental (+) or (-) strands were sequenced. Under non-SOS conditions the TU dimer almost completely blocked replication, while under SOS conditions it directed the incorporation of two As with much higher specificity (96%) than would an abasic site. The implications of these results to the mechanism of the UV-induced TC --> TT mutation, and by extension to the CT --> TT, CC --> TC, CC --> CT, and the tandem CC --> TT mutations, are discussed.