Kim Hyun-Jin, Roux Agnes, Sonenshein Abraham L
Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
Mol Microbiol. 2002 Jul;45(1):179-90. doi: 10.1046/j.1365-2958.2002.03003.x.
Carbon catabolite repression of the Bacillus subtilis citrate synthase (citZ) and aconitase (citB) genes, previously known to be regulated by CcpC, was shown to depend on CcpA as well. Transcription of the citZ gene was partially derepressed in ccpA and ccpC single mutants and fully derepressed in a ccpA ccpC double mutant. DNase I footprinting studies showed that CcpA binds to a catabolite-responsive element (cre) site located at positions +80 to +97 with respect to the transcription start site, whereas CcpC binds at positions -14 to +6 and +16 to +36. Mutations in the citZ cre site greatly altered CcpA binding and repression. A ccpA null mutation also caused partial derepression of citB. Disruption of citrate synthase activity, however, suppressed the effect of the ccpA mutation, suggesting that increased citrate accumulation in a ccpA mutant partially inactivates CcpC and causes partial derepression of citB. Therefore, CcpA controls expression of Krebs cycle genes directly by regulating transcription of citZ and in-directly by regulating availability of citrate, the inducer for CcpC.
枯草芽孢杆菌柠檬酸合酶（citZ）和乌头酸酶（citB）基因的碳分解代谢物阻遏作用，以前已知受CcpC调控，现在发现也依赖于CcpA。citZ基因的转录在ccpA和ccpC单突变体中部分去阻遏，在ccpA ccpC双突变体中完全去阻遏。DNase I足迹分析表明，CcpA结合到相对于转录起始位点位于+80至+97位置的碳分解代谢物反应元件（cre）位点，而CcpC结合在-14至+6和+16至+36位置。citZ cre位点的突变极大地改变了CcpA的结合和阻遏作用。ccpA无效突变也导致citB部分去阻遏。然而，柠檬酸合酶活性的破坏抑制了ccpA突变的影响，这表明ccpA突变体中柠檬酸积累的增加部分地使CcpC失活，并导致citB部分去阻遏。因此，CcpA通过直接调控citZ的转录以及通过调控CcpC的诱导物柠檬酸的可用性间接控制 Krebs 循环基因的表达。
