THE THYMINE-THYMINE PYRIMIDINE-PYRIMIDONE(6-4) ULTRAVIOLET-LIGHT PHOTOPRODUCT IS HIGHLY MUTAGENIC AND SPECIFICALLY INDUCES 3' THYMINE-TO-CYTOSINE TRANSITIONS IN ESCHERICHIA-COLI
THE THYMINE-THYMINE PYRIMIDINE-PYRIMIDONE(6-4) ULTRAVIOLET-LIGHT PHOTOPRODUCT IS HIGHLY MUTAGENIC AND SPECIFICALLY INDUCES 3' THYMINE-TO-CYTOSINE TRANSITIONS IN ESCHERICHIA-COLI
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DOI：
10.1073/pnas.88.21.9685
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发表时间：
1991-11-01
影响因子：
11.1
通讯作者：
LAWRENCE, CW
中科院分区：
文献类型：
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作者：
LECLERC, JE;BORDEN, A;LAWRENCE, CW
我们构建了基于 M13 的单链载体，其中包含特定位置的胸腺嘧啶-胸腺嘧啶-嘧啶酮 (6-4) UV 光产物，并使用这些载体来估计大肠杆菌 uvrA6 细胞中 DNA 复制经过该加合物的频率和准确性。研究了 (6-4) 加合物的正常价光异构体和杜瓦价光异构体。在没有 SOS 诱导的情况下，携带光产物的载体很少被复制；相对于无损伤对照，携带正常(6-4)异构体的载体有1.9%产生噬菌斑，而携带杜瓦价异构体的该比例为0.4%。在 SOS 诱导的细胞中，这些频率分别上升至 22.1% 和 12.3%。 SOS 诱导的细胞中复制超过正常异构体的错误频率很高；在分析的 185 个子代噬菌体的随机样本中，有 169 个（91%）含有突变，所有这些都是有针对性的。同样引人注目的是，很大一部分突变 (158/169；93%) 仅属于一种类型，即 3' T --> C 转换。杜瓦价异构体的错误频率和特异性都大大降低；总体而言，所分析的噬菌体中有 74/140 (53%) 是突变体，其中只有 34 (46%) 需要 3' T --> C 转变。我们推测高错误频率和特异性是由于稳定的 T.G 碱基对的形成引起的，涉及嘧啶酮环中 O-2 和 N-3 处的氢键。这些位点上的潜在氢键在正常异构体中是共面的，但在杜瓦异构体中不是共面的，这也许可以解释后一种加合物诱变特异性降低的原因。
We have constructed single-stranded, M13-based vectors that contain a specifically located thymine-thymine pyrimidine-pyrimidone(6-4) UV photoproduct and have used these to estimate the frequency and accuracy of DNA replication past this adduct in uvrA6 cells of Escherichia coli. Both the normal and the Dewar valence photoisomer of the (6-4) adduct were studied. In the absence of SOS induction, vectors carrying the photoproducts were rarely replicated; relative to the lesion-free control, 1.9% of vectors carrying the normal (6-4) isomer produced plaques, and with the Dewar valence isomer the proportion was 0.4%. In SOS-induced cells, these frequencies rose to 22.1% and 12.3%, respectively. The error frequency of replication past the normal isomer in SOS-induced cells was high; in a random sample of 185 progeny phage analyzed, 169 (91%) contained mutations, all of which were targeted. Equally striking, a high proportion of the mutations (158/169; 93%) were of only one type, namely 3' T --> C transitions. Both the error frequency and the specificity were much reduced with the Dewar valence isomer; overall, 74/140 (53%) of the phage analyzed were mutant, and of these only 34 (46%) entailed the 3' T --> C transition. We speculate that the high error frequency and specificity arise from the formation of a stable T.G base pair, involving hydrogen bonds at O-2 and N-3 in the pyrimidone ring. Potential hydrogen bonds at these sites are coplanar in the normal but not in the Dewar isomer, perhaps explaining the reduced specificity of mutagenesis with the latter adduct.