Shi X, Bennett G N
Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77251.
J Bacteriol. 1994 Nov;176(22):7017-23. doi: 10.1128/jb.176.22.7017-7023.1994.
For Escherichia coli, there have been more and more examples illustrating that the alpha subunit of RNA polymerase is directly involved in the activation of gene transcription by interaction with activator proteins. Because of the vital function of the alpha subunit in cell growth, only a limited number of mutations in its structural gene, rpoA, have been isolated. We obtained a number of these mutants and examined the effects of these mutations on the acid induction of adi and cad gene expression. Several mutations caused a small reduction in adi promoter activity at inducing pH. One mutation, rpoA341, essentially eliminated adi promoter activity, while it had little effect on the cad promoter. During the course of a separate study, we isolated a plasmid that enhanced adi expression. Further characterization of this plasmid showed that it contained cysB, the structural gene for the positive regulator for most cys operon genes. Introduction of a cysB mutation into an adi::lac fusion strain and beta-galactosidase assay studies of the resultant adi::lac cysB mutant established that a wild-type cysB gene was required for efficient acid induction of adi expression. These results suggest that a possible interaction between CysB and the alpha subunit of RNA polymerase is involved in activation of adi transcription.
对于大肠杆菌，越来越多的例子表明，RNA聚合酶的α亚基通过与激活蛋白相互作用直接参与基因转录的激活。由于α亚基在细胞生长中具有重要功能，其结构基因rpoA中仅分离出有限数量的突变。我们获得了一些这些突变体，并研究了这些突变对adi和cad基因表达酸诱导的影响。几个突变在诱导pH下导致adi启动子活性略有降低。一个突变rpoA341基本上消除了adi启动子活性，而对cad启动子几乎没有影响。在另一项研究过程中，我们分离出一个增强adi表达的质粒。对该质粒的进一步表征表明，它含有cysB，这是大多数cys操纵子基因的正调控因子的结构基因。将cysB突变引入adi::lac融合菌株，并对所得的adi::lac cysB突变体进行β-半乳糖苷酶测定研究，结果表明野生型cysB基因是adi表达有效酸诱导所必需的。这些结果表明，CysB与RNA聚合酶α亚基之间可能的相互作用参与了adi转录的激活。
