La Penta D, Zhang X P, Cleary P P
Department of Microbiology, University of Minnesota, Minneapolis 55455.
Mol Microbiol. 1994 Jun;12(6):873-9. doi: 10.1111/j.1365-2958.1994.tb01075.x.
Streptococcus pyogenes is an important agent of human disease which expresses a variety of proteins and polysaccharides on its surface. Surface molecules M protein and streptococcal C5a peptidase (SCPA) are virulence factors which undergo concurrent phase variation and are under the co-ordinate control of the virR locus. Most opacity factor-positive (OF+) strains of S. pyogenes also express IgG Fc receptor proteins on their surface. These studies were initiated to determine whether the type IIa Fc receptor on the surface of S. pyogenes phase-varies with members of this regulatory circuit. Several methods were applied to M+ and M- variant strains to evaluate this question. (i) Immunoblot assays quantified Fc receptors on whole cells by using human IgG myeloma protein and receptor-specific antibody. M+ strains bound IgG and antibody specific for Fc protein, whereas M- strains did not. (ii) Enzyme-linked immunosorbent assays quantified Fc receptor antigen expression and showed that M+ strains produce more Fc receptor protein than their M- derivatives. (iii) Quantitative RNA dot blots showed that the message for the Fc receptor gene (fcrA) was reduced in M- strains. RNA from M+ strains hybridized to the fcrA probe at a greater dilution than that from their M- counterparts. (iv) Northern hybridization showed that the fcrA transcript is 1200 nucleotides in size and distinct from transcripts for M and SCPA proteins. These data are evidence for the co-ordinate transcriptional control of the Fc receptor, M protein, and SCPA and show that these proteins co-ordinately phase-vary within the same regulatory circuit.
化脓性链球菌是人类疾病的重要病原体，其表面表达多种蛋白质和多糖。表面分子M蛋白和链球菌C5a肽酶（SCPA）是毒力因子，它们会同时发生相变，并受virR基因座的协同调控。大多数化脓性链球菌的不透明因子阳性（OF+）菌株在其表面也表达IgG Fc受体蛋白。开展这些研究是为了确定化脓性链球菌表面的IIa型Fc受体是否与该调控回路的成员一起发生相变。应用了几种方法对M+和M-变异菌株进行检测，以评估这个问题。（i）免疫印迹分析通过使用人IgG骨髓瘤蛋白和受体特异性抗体对全细胞上的Fc受体进行定量。M+菌株结合IgG和Fc蛋白特异性抗体，而M-菌株则不结合。（ii）酶联免疫吸附测定对Fc受体抗原表达进行定量，结果显示M+菌株产生的Fc受体蛋白比其M-衍生菌株更多。（iii）定量RNA斑点印迹显示，M-菌株中Fc受体基因（fcrA）的信息减少。来自M+菌株的RNA与fcrA探针杂交时的稀释度比其M-对应菌株更高。（iv）Northern杂交显示，fcrA转录本大小为1200个核苷酸，与M蛋白和SCPA蛋白的转录本不同。这些数据证明了Fc受体、M蛋白和SCPA存在协同转录调控，并表明这些蛋白在同一调控回路中协同发生相变。
