Debarbouille M, Gardan R, Arnaud M, Rapoport G
Unité de Biochimie Microbienne, Institut Pasteur, URA 1300 du Centre National de la Recherche Scientifique, 75724 Paris Cedex 15, France.
J Bacteriol. 1999 Apr;181(7):2059-66. doi: 10.1128/JB.181.7.2059-2066.1999.
A new gene, bkdR (formerly called yqiR), encoding a regulator with a central (catalytic) domain was found in Bacillus subtilis. This gene controls the utilization of isoleucine and valine as sole nitrogen sources. Seven genes, previously called yqiS, yqiT, yqiU, yqiV, bfmBAA, bfmBAB, and bfmBB and now referred to as ptb, bcd, buk, lpd, bkdA1, bkdA2, and bkdB, are located downstream from the bkdR gene in B. subtilis. The products of these genes are similar to phosphate butyryl coenzyme A transferase, leucine dehydrogenase, butyrate kinase, and four components of the branched-chain keto acid dehydrogenase complex: E3 (dihydrolipoamide dehydrogenase), E1alpha (dehydrogenase), E1beta (decarboxylase), and E2 (dihydrolipoamide acyltransferase). Isoleucine and valine utilization was abolished in bcd and bkdR null mutants of B. subtilis. The seven genes appear to be organized as an operon, bkd, transcribed from a -12, -24 promoter. The expression of the bkd operon was induced by the presence of isoleucine or valine in the growth medium and depended upon the presence of the sigma factor SigL, a member of the sigma 54 family. Transcription of this operon was abolished in strains containing a null mutation in the regulatory gene bkdR. Deletion analysis showed that upstream activating sequences are involved in the expression of the bkd operon and are probably the target of bkdR. Transcription of the bkd operon is also negatively controlled by CodY, a global regulator of gene expression in response to nutritional conditions.
在枯草芽孢杆菌中发现了一个新基因bkdR（以前称为yqiR），它编码一种带有中央（催化）结构域的调节因子。该基因控制异亮氨酸和缬氨酸作为唯一氮源的利用。七个基因，以前称为yqiS、yqiT、yqiU、yqiV、bfmBAA、bfmBAB和bfmBB，现在称为ptb、bcd、buk、lpd、bkdA1、bkdA2和bkdB，位于枯草芽孢杆菌中bkdR基因的下游。这些基因的产物与磷酸丁酰辅酶A转移酶、亮氨酸脱氢酶、丁酸激酶以及支链酮酸脱氢酶复合体的四个组分相似：E3（二氢硫辛酰胺脱氢酶）、E1α（脱氢酶）、E1β（脱羧酶）和E2（二氢硫辛酰胺酰基转移酶）。枯草芽孢杆菌的bcd和bkdR缺失突变体中异亮氨酸和缬氨酸的利用被消除。这七个基因似乎被组织成一个操纵子bkd，从一个-12、-24启动子转录。bkd操纵子的表达由生长培养基中异亮氨酸或缬氨酸的存在诱导，并依赖于σ因子SigL（σ54家族的一员）的存在。在调节基因bkdR中含有缺失突变的菌株中，该操纵子的转录被消除。缺失分析表明，上游激活序列参与bkd操纵子的表达，可能是bkdR的作用靶点。bkd操纵子的转录也受到CodY的负调控，CodY是一种响应营养条件的全局基因表达调节因子。
