Elledge S J, Walker G C
J Bacteriol. 1983 Sep;155(3):1306-15. doi: 10.1128/jb.155.3.1306-1315.1983.
A gene fusion was constructed in vitro that resulted in the synthesis of a hybrid protein consisting of the amino-terminal segment of the MucB protein of the mutagenesis-enhancing plasmid pKM101 joined to an enzymatically active carboxy-terminal segment of the beta-galactosidase protein. In strains bearing this fusion, beta-galactosidase activity was induced by UV radiation and other DNA-damaging agents. A genetic analysis of the regulation of expression of the phi (mucB'-lacZ') fusion was consistent with the LexA protein acting as the direct repressor of the mucB gene. Examination of the expression of the mucA and phi (mucB'-lacZ') gene products in maxicells in the presence and absence of a high-copy-number plasmid carrying the lexA+ gene demonstrated that lexA regulated both the mucA and mucB genes, thus supporting our conclusion that the two genes are organized in an operon with the mucA gene transcribed first. An analysis of the effects of the recA430(lexB30) mutation on muc expression led to the discovery of the differential ability of the recA430 gene product to induce expression of a dinB::Mu d1(Ap lac) fusion located on the chromosome and the same phi (dinB'-lacZ+) fusion cloned into plasmid pBR322. Models to account for the role of the recA430 allele on the expression of damage-inducible genes and on mutagenesis are discussed.
在体外构建了一种基因融合体，其结果是合成了一种杂合蛋白，该杂合蛋白由诱变增强质粒pKM101的MucB蛋白的氨基末端片段与β-半乳糖苷酶蛋白的具有酶活性的羧基末端片段连接而成。在携带这种融合体的菌株中，β-半乳糖苷酶活性可由紫外线辐射和其他DNA损伤剂诱导。对φ（mucB'-lacZ'）融合体表达调控的遗传分析与LexA蛋白作为mucB基因的直接阻遏物的作用一致。在存在和不存在携带lexA +基因的高拷贝数质粒的情况下，对maxicells中mucA和φ（mucB'-lacZ'）基因产物的表达进行检测，结果表明lexA对mucA和mucB基因均有调控作用，从而支持了我们的结论，即这两个基因组成一个操纵子，其中mucA基因先转录。对recA430（lexB30）突变对muc表达的影响进行分析，发现recA430基因产物诱导位于染色体上的dinB::Mu d1（Ap lac）融合体和克隆到质粒pBR322中的相同φ（dinB'-lacZ +）融合体表达的能力存在差异。文中讨论了解释recA430等位基因在损伤诱导基因表达和诱变作用中所起作用的模型。
