Renna M C, Najimudin N, Winik L R, Zahler S A
Section of Genetics and Development, Cornell University, Ithaca, New York 14853.
J Bacteriol. 1993 Jun;175(12):3863-75. doi: 10.1128/jb.175.12.3863-3875.1993.
Acetoin is a major extracellular product of Bacillus subtilis grown on glucose and other fermentable carbon sources. The enzymes responsible for the formation of acetoin, acetolactate synthase, and acetolactate decarboxylase are synthesized in detectable amounts only in cells that have reached stationary phase. We have cloned and sequenced the genes encoding these enzymes, alsS and alsD, as well as a gene, alsR, that regulates their expression. alsS and alsD appear to compose a single operon, while alsR is transcribed divergently from the alsSD operon. AlsR shows significant homology to the LysR family of bacterial activator proteins, and when alsR is disrupted the alsSD operon is not expressed. Transcriptional fusions to alsS and alsR revealed that AlsR is required for the transcription of the alsSD operon, which increases during stationary phase. Two mutations that cause increased expression of the alsSD operon have been isolated, cloned, and sequenced. They each change an amino acid in the AlsR protein.
乙偶姻是枯草芽孢杆菌在葡萄糖和其他可发酵碳源上生长时产生的一种主要胞外产物。负责乙偶姻形成的酶，即乙酰乳酸合酶和乙酰乳酸脱羧酶，只有在进入稳定期的细胞中才会以可检测到的量合成。我们已经克隆并测序了编码这些酶的基因alsS和alsD，以及一个调控它们表达的基因alsR。alsS和alsD似乎组成一个单一的操纵子，而alsR则从alsSD操纵子反向转录。AlsR与细菌激活蛋白的LysR家族具有显著的同源性，当alsR被破坏时，alsSD操纵子不表达。与alsS和alsR的转录融合表明，AlsR是alsSD操纵子转录所必需的，该操纵子在稳定期表达增加。已经分离、克隆并测序了两个导致alsSD操纵子表达增加的突变。它们各自改变了AlsR蛋白中的一个氨基酸。
