Palejwala V A, Rzepka R W, Humayun M Z
Department of Microbiology and Molecular Genetics, UMD-New Jersey Medical School, Newark 07103.
Biochemistry. 1993 Apr 20;32(15):4112-20. doi: 10.1021/bi00066a037.
Mutagenic action of chemical and physical mutagens is mediated through DNA damage and subsequent misreplication at sites of unrepaired damage. Most DNA damage is noninstructive in the sense that the causative chemical modification either destroys the template information or renders it inaccessible to the DNA polymerase. Noninstructive adducts possess high genotoxicity because they stop DNA replication. Replication past noninstructive adducts is thought to depend on induced functions in addition to the regular replication machinery. In Escherichia coli, noninstructive DNA damage leads to induction of the SOS regulon, which in turn is thought to provide the inducible functions required for replicative bypass of the lesion. Because of the absence of accessible template instruction, base incorporation opposite noninstructive lesions is inherently error-prone and results in mutagenesis. Ethenocytosine (epsilon C), an exocyclic DNA lesion induced by carcinogens such as vinyl chloride and urethane, is a highly mutagenic, noninstructive lesion on the basis of its template characteristics in vivo and in vitro. However, mutagenesis at epsilon C does not require SOS functions, as evidenced by efficient mutagenesis in recA-deleted E. coli. Even though efficient mutagenesis in recA-deleted cells shows a lack of SOS dependence, the question remains whether SOS induction can modulate mutagenesis opposite epsilon C. To examine the possible contribution of SOS functions to mutagenesis at epsilon C, we constructed an M13 duplex circular DNA molecule containing an epsilon C residue at a unique site. The construct was transfected into nonirradiated or UV-irradiated E. coli.(ABSTRACT TRUNCATED AT 250 WORDS)
化学和物理诱变剂的诱变作用是通过DNA损伤以及随后在未修复损伤位点的错误复制来介导的。大多数DNA损伤是非指令性的，因为引起损伤的化学修饰要么破坏模板信息，要么使DNA聚合酶无法获取该信息。非指令性加合物具有很高的遗传毒性，因为它们会阻止DNA复制。越过非指令性加合物的复制被认为除了依赖常规的复制机制外，还依赖诱导功能。在大肠杆菌中，非指令性DNA损伤会导致SOS调节子的诱导，而SOS调节子又被认为提供了损伤复制旁路所需的诱导功能。由于缺乏可获取的模板指令，在非指令性损伤对面掺入碱基本质上就容易出错，并导致诱变。乙烯基胞嘧啶（εC）是一种由氯乙烯和聚氨酯等致癌物诱导产生的环外DNA损伤，根据其在体内和体外的模板特性，它是一种高度诱变的非指令性损伤。然而，εC处的诱变并不需要SOS功能，recA缺失的大肠杆菌中高效诱变就证明了这一点。尽管recA缺失细胞中的高效诱变表明缺乏对SOS的依赖性，但SOS诱导是否能调节εC对面的诱变这一问题仍然存在。为了研究SOS功能对εC处诱变的可能贡献，我们构建了一个M13双链环状DNA分子，该分子在一个独特位点含有一个εC残基。将该构建体转染到未辐照或紫外线辐照的大肠杆菌中。（摘要截短于250字）
