Transcriptional regulation of GBS capsule biosynthesis

描述（由申请人提供）：无乳链球菌（B群链球菌或GBS）是新生儿肺炎，败血症和脑膜炎的常见原因。荚膜GBS突变体在小鼠中表现出毒性下降，表明荚膜多糖是主要的毒力因子。发现GBS菌株表达9种不同的胶囊血清型，Ia， Ib和II-VIII。我们的研究重点是GBS胶囊在人类感染中最重要的血清型之一，Ia型。指导Ia型胶囊合成的GBS操纵子由16个基因组成，预计包含两个启动子。第一个启动子位于第一个基因cpsIaA的上游。第二个下游启动子预计位于cpsIaE的上游。非极性cpsIaA缺失突变体在细胞表面的荚膜表达减少，但cpsIaA缺失突变体及其亲本野生型菌株的单个荚膜链分子大小相同。此外，cpsIaA缺失突变体中cpsIaA下游基因的转录下调。这些结果提示CpsIaA作为转录激活剂。在这个提议中，我们将确定Ia型GBS胶囊操纵子的转录组织和相对启动子强度。此外，我们将确定CpsIaA是否直接调节Ia型胶囊基因的转录。本提案中概述的实验将有助于更好地理解GBS胶囊生物合成的转录调控。

DESCRIPTION (provided by applicant): Streptococcus agalactiae (Group B Streptococcus or GBS) is a common cause of neonatal pneumonia, sepsis and meningitis. Acapsular GBS mutants exhibit decreased virulence in mice suggesting that the capsular polysaccharide is a major virulence factor. Strains of GBS are found to express nine different capsule serotypes, Ia, Ib and II-VIII. We have focused our study on one of the most important in GBS capsule serotypes in human infection, type Ia. The GBS operon that directs synthesis of the type Ia capsule consists of 16 genes and is predicted to contain two promoters. The first promoter is upstream of the first gene, cpsIaA. A second, downstream promoter is predicted to lie upstream of cpsIaE. A non-polar cpsIaA deletion mutant exhibits decreased capsule expression at the surface of the cell, yet individual capsule chains in the cpsIaA deletion mutant and its parent wild-type strain are the same molecular size. Additionally, transcription of genes downstream of cpsIaA is down-regulated in a cpsIaA deletion mutant. These results are suggestive of CpsIaA acting as a transcriptional activator. In this proposal we will determine the transcriptional organization and relative promoter strength of the type Ia GBS capsule operon. In addition, we will determine if CpsIaA directly modulates transcription of the type Ia capsule genes. Experiments outlined in this proposal will lead to a better understanding of transcriptional regulation of GBS capsule biosynthesis.