McIver K S, Heath A S, Green B D, Scott J R
Department of Microbiology and Immunology, Rollins Research Center, Emory University, Atlanta, Georgia 30322, USA.
J Bacteriol. 1995 Nov;177(22):6619-24. doi: 10.1128/jb.177.22.6619-6624.1995.
Transcription of the surface-associated virulence factors of the group A streptococcus (GAS) Streptococcus pyogenes, M protein (emm) and the C5a peptidase (scpA), is activated by a protein called Mga (formerly Mry or VirR). To determine whether Mga binds directly to the promoters of the genes it regulates, a protein resulting from the fusion of Mga to the C-terminal end of maltose-binding protein was purified from Escherichia coli. Specific binding to the promoter regions of the scpA and emm alleles of the type M6 GAS strain JRS4 was demonstrated by electrophoresis of the DNA-protein complex. Competition studies showed that the region upstream of scpA bound MBP-Mga with a slightly higher affinity than did the region upstream of emm. DNase I protection experiments identified a single 45-bp binding site immediately upstream of and overlapping the -35 region of both promoters. Sequences homologous to the protected regions were found in the promoters of many emm, scp, and emm-like genes from strains of different serotypes of GAS, and a consensus Mga binding site was deduced.
A群链球菌（GAS）化脓性链球菌的表面相关毒力因子M蛋白（emm）和C5a肽酶（scpA）的转录由一种名为Mga（以前称为Mry或VirR）的蛋白质激活。为了确定Mga是否直接结合其调控基因的启动子，从大肠杆菌中纯化了一种由Mga与麦芽糖结合蛋白C末端融合产生的蛋白质。通过DNA-蛋白质复合物的电泳证明了其与M6型GAS菌株JRS4的scpA和emm等位基因启动子区域的特异性结合。竞争研究表明，scpA上游区域与MBP-Mga的结合亲和力略高于emm上游区域。DNase I保护实验在两个启动子的-35区域上游紧邻且重叠处鉴定出一个单一的45 bp结合位点。在来自不同血清型GAS菌株的许多emm、scp和emm样基因的启动子中发现了与受保护区域同源的序列，并推导了一个共有Mga结合位点。
