Chen P, Ailion M, Bobik T, Stormo G, Roth J
Biology Department, University of Utah, Salt Lake City 84112, USA.
J Bacteriol. 1995 Oct;177(19):5401-10. doi: 10.1128/jb.177.19.5401-5410.1995.
Propanediol is degraded by a B12-dependent pathway in Salmonella typhimurium. The enzymes for this pathway are encoded in a small region (minute 41) that includes the pdu operon (controlling B12-dependent degradation of propanediol) and the divergent cob operon (controlling synthesis of cobalamin, B12). Expression of both operons is induced by propanediol and globally controlled by the ArcA and Crp systems. The region between the two operons encodes two proteins, PduF, a transporter of propanediol, and PocR, which mediates the induction of the regulon by propanediol. Insertion mutations between the pdu and cob operons have been characterized, and their exact positions have been correlated with mutant phenotypes. The region includes five promoters, four of which are controlled by the PocR protein and induced by propanediol. The cob and pdu operons each have one regulated promoter; the pduF gene is expressed from two regulated promoters (P1 and P2). The P1 and P2 transcripts extend beyond pduF to include the pocR gene; thus the PocR protein autoregulates its expression from these promoters. The fifth promoter, PPoc, is adjacent to the pocR gene and associated with a Crp binding site. We suggest that all global control of the regulon is exerted by regulating the level of PocR protein at the P1, P2, and PPoc promoters. A putative binding site for the PocR protein has been identified by computer analysis. Eight close matches to this proposed site were found in regions near the four promoters known to be regulated by PocR protein: PPdu, P1, P2, and PCob. A three-state model is proposed in which the regulon uses all five of its promoters to control expression.
在鼠伤寒沙门氏菌中，丙二醇通过一条依赖维生素B12的途径被降解。该途径的酶由一个小区域（41分钟处）编码，该区域包括pdu操纵子（控制丙二醇的维生素B12依赖性降解）和反向的cob操纵子（控制钴胺素即维生素B12的合成）。两个操纵子的表达均由丙二醇诱导，并受ArcA和Crp系统的全局调控。两个操纵子之间的区域编码两种蛋白质，丙二醇转运蛋白PduF和介导丙二醇对调节子诱导作用的PocR。已对pdu和cob操纵子之间的插入突变进行了表征，其确切位置与突变表型相关。该区域包括五个启动子，其中四个受PocR蛋白控制并由丙二醇诱导。cob和pdu操纵子各有一个受调控的启动子；pduF基因由两个受调控的启动子（P1和P2）表达。P1和P2转录本延伸至pduF之外，包括pocR基因；因此，PocR蛋白从这些启动子自动调节其自身表达。第五个启动子PPoc与pocR基因相邻，并与一个Crp结合位点相关。我们认为，调节子的所有全局调控都是通过调节P1、P2和PPoc启动子处的PocR蛋白水平来实现的。通过计算机分析确定了PocR蛋白的一个假定结合位点。在已知受PocR蛋白调控的四个启动子（PPdu、P1、P2和PCob）附近的区域中发现了与该假定位点的八个紧密匹配。提出了一个三态模型，其中调节子利用其所有五个启动子来控制表达。
