Keener J, Nomura M
Department of Biological Chemistry, University of California, Irvine 92717.
Proc Natl Acad Sci U S A. 1993 Mar 1;90(5):1751-5. doi: 10.1073/pnas.90.5.1751.
A dominant lethal mutation in the Escherichia coli rpoD gene, which encodes sigma 70, the promoter recognition subunit of RNA polymerase, was isolated after random mutagenesis. The lethal gene was maintained under control of the lac repressor on a low copy plasmid. An amount of lethal sigma 70 that was nearly equimolar with the chromosomally encoded sigma 70 was sufficient to cause cessation of growth. RNA synthesis per unit cell mass was unaffected, but protein synthesis was inhibited by the mutant sigma 70. The amino acid change (Glu-585 to Gln) was in a region of sigma 70 thought to bind the -35 hexamer of the promoter, and the mutant sigma 70 caused increased expression from promoters with nonconsensus bases in the third position of the -35 hexamer. A null mutation of the fis gene could partially suppress the mutant phenotype. These properties are consistent with those expected of a sigma 70 insensitive to growth rate control of rRNA and tRNA promoters.
在随机诱变后，分离出了大肠杆菌rpoD基因中的一个显性致死突变，该基因编码RNA聚合酶的启动子识别亚基σ70。致死基因在低拷贝质粒上的乳糖阻遏物控制下得以维持。与染色体编码的σ70几乎等摩尔的致死性σ70足以导致生长停止。单位细胞质量的RNA合成未受影响，但蛋白质合成受到突变型σ70的抑制。氨基酸变化（Glu-585变为Gln）位于σ70中一个被认为与启动子的-35六聚体结合的区域，并且突变型σ70导致在-35六聚体第三位具有非一致碱基的启动子的表达增加。fis基因的无效突变可部分抑制突变表型。这些特性与对rRNA和tRNA启动子的生长速率控制不敏感的σ70所预期的特性一致。
