Analysis of interaction between the competence transcription factor, ComK and its regulatory factor, Med

枯草芽孢杆菌能力的主调控因子ComK是后期能力操作子转录所必需的。ComK在与MecA和ClpC的复合体中无活性，但在ComS的作用下从复合体中释放后被激活。已发现Med是MecA下游comK功能的正向调节因子。它是一种被认为具有脂质修饰信号的脂蛋白。碱性磷酸酶与Med融合和Western分析显示Med位于细胞膜外表面。Western和Northern分析显示med突变体的ComK降低。未磷酸化的DegU是DegS-DegU双组分系统调节外蛋白酶产生的应答调节剂，是comK转录所必需的，而磷酸化的DegU是外蛋白酶产生所必需的。med突变的作用被degS的缺失所抑制，表明med可以调节DegU的磷酸化，即抑制DegU磷酸化的因子可能通过med依赖的方式被掺入。我们发现，多拷贝phrG抑制了pre - lacz的表达，导致comK转录增加。在培养物中加入合成的PhrG五肽可降低pre - lacz的表达。这些结果提示phrG可能通过DegU正向调节comK的转录。PhrC五肽的群体感应调节导致反应调节因子ComA的激活，从而触发comS的转录。除RapC-PhrC外，RapG-PhrG还被鉴定为coma控制基因表达的调控系统。

A master regulator for B. subtilis competence, ComK, is required for transcription of late competence operons. ComK is inactive in a complex with MecA and ClpC, but is activated upon release from the complex by the action of ComS.Med has been found as a positive regulator for comK functioning downstream from MecA. It is a putative lipoprotein with a lipid modification signal. An alkaline phosphatase fusion with Med and Western analysis revealed localization of Med on the outer surface of the cell membrane.Western and Northern analyses showed a decrease of ComK in the med mutant. Unphosphorylated DegU, a response regulator of the DegS-DegU two-component system regulating exoprotease production, is necessary for transcription of comK, whereas phosphoryrlated DegU is necessary for exoprotease production. The effect of the med mutation was suppressed by deletion of degS, suggesting that Med could modulate DegU phosphorylation, I.e., a factor inhibiting DegU phosphorylation might be incorporated by a Med-dependent manner. We have found that multicopy phrG inhibited the expression of aprE-lacZ and caused an increase in comK transcription. Addition of a synthetic PhrG pentapeptide to the culture reduced aprE-lacZ expression. These results suggested that phrG positively regulates transcription of comK possibly through DegU.Quorum sensing regulation by the PhrC pentapeptide results in activation of a response regulator, ComA, triggering transcription of comS. RapG-PhrG was also identified as the regulatory system for expression of the ComA-controlled genes in addition to RapC-PhrC.