Tobisch S, Stülke J, Hecker M
Institut für Mikrobiologie und Molekularbiologie, Ernst-Moritz-Arndt-Universität Greifswald, D-17487 Greifswald, Germany.
J Bacteriol. 1999 Aug;181(16):4995-5003. doi: 10.1128/JB.181.16.4995-5003.1999.
The lic operon of Bacillus subtilis is required for the transport and degradation of oligomeric beta-glucosides, which are produced by extracellular enzymes on substrates such as lichenan or barley glucan. The lic operon is transcribed from a sigma(A)-dependent promoter and is inducible by lichenan, lichenan hydrolysate, and cellobiose. Induction of the operon requires a DNA sequence with dyad symmetry located immediately upstream of the licBCAH promoter. Expression of the lic operon is positively controlled by the LicR regulator protein, which contains two potential helix-turn-helix motifs, two phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) regulation domains (PRDs), and a domain similar to PTS enzyme IIA (EIIA). The activity of LicR is stimulated by modification (probably phosphorylation) of both PRD-I and PRD-II by the general PTS components and is negatively regulated by modification (probably phosphorylation) of its EIIA domain by the specific EII(Lic) in the absence of oligomeric beta-glucosides. This was shown by the analysis of licR mutants affected in potential phosphorylation sites. Moreover, the lic operon is subject to carbon catabolite repression (CCR). CCR takes place via a CcpA-dependent mechanism and a CcpA-independent mechanism in which the general PTS enzyme HPr is involved.
枯草芽孢杆菌的lic操纵子对于低聚β-葡萄糖苷的转运和降解是必需的，低聚β-葡萄糖苷由胞外酶作用于诸如地衣多糖或大麦葡聚糖等底物产生。lic操纵子从一个依赖于σ(A)的启动子转录，并且可被地衣多糖、地衣多糖水解产物和纤维二糖诱导。该操纵子的诱导需要一个位于licBCAH启动子上游紧邻处的具有二元对称的DNA序列。lic操纵子的表达受到LicR调节蛋白的正调控，LicR含有两个潜在的螺旋-转角-螺旋基序、两个磷酸烯醇丙酮酸：碳水化合物磷酸转移酶系统（PTS）调节结构域（PRD）以及一个类似于PTS酶IIA（EIIA）的结构域。LicR的活性受到一般PTS组分对PRD-I和PRD-II的修饰（可能是磷酸化）的刺激，并且在没有低聚β-葡萄糖苷的情况下，受到特异性EII(Lic)对其EIIA结构域的修饰（可能是磷酸化）的负调控。这通过对潜在磷酸化位点发生改变的licR突变体的分析得以证明。此外，lic操纵子受到碳分解代谢物阻遏（CCR）的影响。CCR通过一种依赖于CcpA的机制和一种涉及一般PTS酶HPr的不依赖于CcpA的机制发生。
