Crater D L, van de Rijn I
Wake Forest University Medical Center, Winston-Salem, North Carolina 27157, USA.
J Biol Chem. 1995 Aug 4;270(31):18452-8. doi: 10.1074/jbc.270.31.18452.
The has operon is composed of three genes, hasA, hasB, and hasC that encode hyaluronate synthase, UDP-glucose dehydrogenase, and presumptively UDP-glucose pyrophosphorylase, respectively. Expression of the has operon was shown to be required for the synthesis of the hyaluronic acid capsule in group A streptococci. Previous studies indicated that some group A and group C streptococcal strains produce the hyaluronic acid capsule, while others do not. In addition, it was observed that encapsulated strains cultured in stationary phase of growth lose the hyaluronic acid capsule. Therefore, the molecular mechanisms controlling the expression of the hyaluronic acid capsule in group A streptococci was investigated. In this study, it was determined that all encapsulated and unencapsulated strains of group A streptococci as well as encapsulated group C streptococci analyzed possess the has operon locus. The acapsular phenotype was accounted for by the absence of hyaluronate synthase activity in the membrane and not the production of extracellular hyaluronidase. A has operon mRNA transcript was not expressed by unencapsulated strains of group A streptococci, whereas encapsulated strains of group A streptococci grown to mid to late exponential phase produced the hyaluronate capsule, as well as has operon mRNA. However, as the streptococci entered the stationary phase of growth, they became acapsular and this was concomitant with the loss of has operon mRNA transcript. These results were confirmed by primer extension analyses of RNA isolated from encapsulated and unencapsulated strains of group A streptococci as well as RNA prepared from encapsulated strains cultured in exponential and stationary phases of growth. Thus, the loss of has operon mRNA in unencapsulated group A streptococci, as well as growth phase regulation occurs at the previously mapped has operon promoter. These data suggested that the synthesis of the hyaluronic acid capsule for group A streptococci may be controlled by transcriptional mechanisms.
has操纵子由三个基因hasA、hasB和hasC组成，它们分别编码透明质酸合酶、UDP-葡萄糖脱氢酶以及推测的UDP-葡萄糖焦磷酸化酶。已证明has操纵子的表达是A组链球菌中透明质酸荚膜合成所必需的。先前的研究表明，一些A组和C组链球菌菌株能产生透明质酸荚膜，而其他菌株则不能。此外，还观察到在生长稳定期培养的有荚膜菌株会失去透明质酸荚膜。因此，对A组链球菌中控制透明质酸荚膜表达的分子机制进行了研究。在本研究中，已确定所分析的所有A组链球菌的有荚膜和无荚膜菌株以及C组有荚膜链球菌都拥有has操纵子位点。无荚膜表型是由于膜中缺乏透明质酸合酶活性，而不是由于细胞外透明质酸酶的产生。A组链球菌的无荚膜菌株不表达has操纵子mRNA转录本，而生长至指数中期到后期的A组链球菌有荚膜菌株会产生透明质酸荚膜以及has操纵子mRNA。然而，随着链球菌进入生长稳定期，它们变得无荚膜，这与has操纵子mRNA转录本的丧失是同时发生的。从A组链球菌的有荚膜和无荚膜菌株分离的RNA以及从处于指数生长期和稳定期培养的有荚膜菌株制备的RNA进行的引物延伸分析证实了这些结果。因此，A组链球菌无荚膜菌株中has操纵子mRNA的丧失以及生长阶段调控发生在先前定位的has操纵子启动子处。这些数据表明，A组链球菌透明质酸荚膜的合成可能受转录机制控制。
