Li B H, Kwasniewski M, Kirchner J, Bockrath R
Indiana University School of Medicine, Indianapolis 46202.
Mol Gen Genet. 1992 Feb;231(3):480-4. doi: 10.1007/BF00292719.
Expression of the lacZ gene in Escherichia coli is inactivated by exposure to ultraviolet light (UV). Inactivation is exceptionally effective when cells contain amplified levels of DNA photolyase (which forms complexes with pyrimidine dimers in the absence of light for actual photoreversal) and a lambda prophage. Without amplified photolyase, the lambda prophage or both, inactivation rates are similar and much lower. UV-inactivation of lacZ gene expression in the presence of both amplified photolyase and lambda is even more effective if lambda cI857 is used in place of the wildtype prophage but is wholly unexceptional if the prophage carries defects in the lambda genes rexA or rexB. When Rex AB proteins are provided by expression from a plasmid and the cell also contains amplified photolyase, exceptional inactivation rates again obtain; in fact inactivation is most effective under these conditions. The data are considered to reveal a role for Rex AB proteins, which mediate superinfection exclusion, in the exceptional inactivation of gene expression by photolyase bound to pyrimidine dimers in DNA. Photolyase-dimer complexes may mimic the structure of certain complexes that arise during phage development and thus influence Rex A and/or B proteins, thereby shutting down cell metabolism.
在大肠杆菌中，lacZ基因的表达会因暴露于紫外线（UV）而失活。当细胞含有扩增水平的DNA光解酶（其在无光条件下与嘧啶二聚体形成复合物以进行实际的光逆转）和λ原噬菌体时，失活异常有效。在没有扩增的光解酶、λ原噬菌体或两者都没有的情况下，失活率相似且低得多。如果使用λcI857代替野生型原噬菌体，在同时存在扩增的光解酶和λ的情况下，lacZ基因表达的紫外线失活甚至更有效，但如果原噬菌体在λ基因rexA或rexB中存在缺陷，则完全没有异常。当通过质粒表达提供Rex AB蛋白且细胞还含有扩增的光解酶时，再次获得异常的失活率；事实上，在这些条件下失活最为有效。这些数据被认为揭示了介导超感染排除的Rex AB蛋白在与DNA中嘧啶二聚体结合的光解酶对基因表达的异常失活中的作用。光解酶 - 二聚体复合物可能模拟噬菌体发育过程中出现的某些复合物的结构，从而影响Rex A和/或B蛋白，进而关闭细胞代谢。
