Shafikhani Sasha H, Núñez Esperanza, Leighton Terrance
Department of Molecular and Cellular Biology, Division of Biochemistry and Molecular Biology, University of California, Berkeley, California 94720, USA.
Curr Microbiol. 2003 Oct;47(4):327-36. doi: 10.1007/s00284-002-4013-1.
Sporulation in Bacillus subtilis can be triggered by carbon catabolite limitation. Conversely, carbon source excess can repress the production of extracellular enzymes, motility, and sporulation. Recent studies have implicated a pH-sensing mechanism, involving AbrB, the TCA cycle, Spo0K, and sigmaH in controlling the catabolite repression of sporulation gene expression. In an accompanying paper, we demonstrate that the AbrB-dependent pH-sensing mechanism may not be the only means by which carbon catabolites affect sporulation. In the studies reported here, we have examined the molecular basis underlying the catabolite repression phenotype of mutations in the hpr (scoC), rpoD (crsA47), and spo0A (rvtA11) loci. Loss of function mutations in hpr (scoC) restored sporulation gene expression and sporulation in the presence of excess catabolite(s), suggesting that Hpr (ScoC) has a pivotal role in mediating catabolite repression. Moreover, hpr gene expression increased substantially in the presence of excess catabolite(s), further supporting the involvement of Hpr (ScoC) in the carbon catabolite response system. We suggest that alterations in the phosphorelay response to catabolites may be one mechanism by which catabolite-resistant mutants such as crsA and rvtA are able to sporulate in the presence of excess glucose.
枯草芽孢杆菌中的孢子形成可由碳分解代谢物限制触发。相反，碳源过量会抑制细胞外酶的产生、运动性和孢子形成。最近的研究表明，一种pH感应机制，涉及AbrB、三羧酸循环、Spo0K和sigmaH，在控制孢子形成基因表达的分解代谢物阻遏中起作用。在一篇配套论文中，我们证明依赖AbrB的pH感应机制可能不是碳分解代谢物影响孢子形成的唯一方式。在此报道的研究中，我们研究了hpr（scoC）、rpoD（crsA47）和spo0A（rvtA11）基因座突变的分解代谢物阻遏表型背后的分子基础。hpr（scoC）功能丧失突变在存在过量分解代谢物的情况下恢复了孢子形成基因表达和孢子形成，这表明Hpr（ScoC）在介导分解代谢物阻遏中起关键作用。此外，在存在过量分解代谢物的情况下，hpr基因表达大幅增加，进一步支持Hpr（ScoC）参与碳分解代谢物反应系统。我们认为，对分解代谢物的磷酸化传递反应的改变可能是诸如crsA和rvtA等抗分解代谢物突变体能够在过量葡萄糖存在下形成孢子的一种机制。
