ALLELIC POLYMORPHISM OF EMM LOCI PROVIDES EVIDENCE FOR HORIZONTAL GENE SPREAD IN GROUP-A STREPTOCOCCI
ALLELIC POLYMORPHISM OF EMM LOCI PROVIDES EVIDENCE FOR HORIZONTAL GENE SPREAD IN GROUP-A STREPTOCOCCI
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DOI：
10.1073/pnas.91.8.3280
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发表时间：
1994-04-12
影响因子：
11.1
通讯作者：
HOLLINGSHEAD, SK
中科院分区：
文献类型：
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作者：
BESSEN, DE;HOLLINGSHEAD, SK
A组链球菌有一个毒力调节子，含有一个emm基因座或两个或三个结构上相关的emm家族基因的不同或相邻基因座。Emm基因簇的产物由纤维状表面蛋白组成，其中至少有一些已知含有位于其NH-2末端的类型特异性决定因素，位于细胞表面的远端。根据EMM基因3‘端编码区的结构差异，EMM基因可分为四个主要的亚家族。在这项研究中，我们调查了代表不同血清型的22株菌株的sf-4和sf-3emm基因5‘端(分别位于基因灰尘的第一和最后emm位置)的多态性。我们的发现表明，与位于中心位置的SF-1或SF-2基因不同，SF-3和SF-4基因在各自的5‘端仅表现出有限的多态性，提示它们的基因产物可能不是类型特异性的主要贡献者。在所有四种可能的组合(SF3(A)SF4(A)、SF3(A)SF4(B)、SF3(B)SF4(A)、SF3(B)SF4(B))中都发现存在两种形式的SF-3基因(SF3a、SF3b)和两种形式的SF-4基因(SF4a、SF4b)，这有力地表明水平基因扩散有助于A组链球菌emm基因的进化和emm基因多样性的产生。
Group A streptococci have a virulence regulon containing a single emm locus or two or three distinct and adjacent loci of structurally related emm family genes. The products of the emm gene cluster consist of fibrillar surface proteins, at least some of which are known to contain determinants of type specificity located in their NH-2-terminal regions, lying distal to the cell surface. The emm genes can be categorized into four major subfamilies (SFs), based on structural differences within their 3' regions encoding the peptidoglycan-spanning domain. In this study, we investigate the polymorphism within the 5' region of SF-4 and SF-3 emm genes (which occupy the first and last emm positions of the gene duster, respectively) in 22 strains- representing different serotypes. Our findings indicate that unlike the centrally positioned SF-1 or SF-2 genes, SF-3 and SF-4 genes each display only limited polymorphism in their 5' regions, suggesting that their gene products may not be major contributors to type specificity. Two forms of the SF-3 gene (SF3a, SF3b) and two forms of the SF-4 gene (SF4a, SF4b) are found to exist in all four possible combinations (SF3(a)SF4(a), SF3(a)SF4(b), SF3(b)SF4(a), SF3(b)SF4(b)), strongly suggesting that horizontal gene spread has contributed to the evolution of emm genes and to the generation of emm gene diversity in group A streptococci.