Shivers Robert P, Dineen Sean S, Sonenshein Abraham L
Department of Molecular Biology and Microbiology, School of Medicine, Tufts University, Boston, MA, USA.
Mol Microbiol. 2006 Nov;62(3):811-22. doi: 10.1111/j.1365-2958.2006.05410.x. Epub 2006 Sep 21.
Conversion of pyruvate to acetate via the phosphotransacetylase-acetate kinase pathway generates ATP and is a major overflow pathway under conditions of carbon and nitrogen excess. In Bacillus subtilis, this pathway is positively regulated by CcpA, a global regulator of carbon metabolism genes. Transcription of the acetate kinase gene (ackA) proved to be activated as well by a second global regulatory protein, CodY. Expression of an ackA-lacZ fusion was reduced in a codY mutant strain. CodY was found to bind in vitro to two sites in the ackA promoter region and to stimulate ackA transcription in a run-off transcription assay. This is the first known case of direct positive regulation by CodY. CodY and CcpA were found to bind to neighbouring sites and their effects were additive both in vivo and in vitro. Surprisingly, positive regulation by CodY, unlike repression, responded primarily to only one type of effector molecule. That is, branched-chain amino acids (BCAAs) served as more potent co-activators of CodY-dependent ackA transcription than did GTP. Given the roles of CcpA and CodY in regulating genes whose products determine the metabolic fate of pyruvate, these two proteins may act together to mediate a hierarchical conversion of pyruvate to its many potential products.
通过磷酸转乙酰酶 - 乙酸激酶途径将丙酮酸转化为乙酸可产生ATP，并且在碳和氮过量的条件下是主要的溢流途径。在枯草芽孢杆菌中，该途径受到CcpA的正向调控，CcpA是碳代谢基因的全局调节因子。事实证明，乙酸激酶基因（ackA）的转录也受到另一种全局调节蛋白CodY的激活。在codY突变菌株中，ackA - lacZ融合蛋白的表达降低。发现CodY在体外与ackA启动子区域的两个位点结合，并在径流转录试验中刺激ackA转录。这是已知的CodY直接正向调控的首例。发现CodY和CcpA与相邻位点结合，并且它们在体内和体外的作用都是相加的。令人惊讶的是，与阻遏作用不同，CodY的正向调控主要仅对一种效应分子作出反应。也就是说，与GTP相比，支链氨基酸（BCAAs）作为CodY依赖性ackA转录的更有效的共激活剂。鉴于CcpA和CodY在调节其产物决定丙酮酸代谢命运的基因中的作用，这两种蛋白质可能共同作用以介导丙酮酸向其许多潜在产物的分级转化。
