Hollingshead S K, Arnold J, Readdy T L, Bessen D E
Department of Microbiology, University of Alabama at Birmingham.
Mol Biol Evol. 1994 Mar;11(2):208-19. doi: 10.1093/oxfordjournals.molbev.a040103.
The emm genes are members of a gene family in group A streptococci (GAS) that encode for antiphagocytic cell-surface proteins and/or immunoglobulin-binding proteins. Previously sequenced genes in this family have been named "emm," "fcrA," "enn," "arp," "protH," and "mrp"; herein they will be referred to as the "emm gene family." The genes in the emm family are located in a cluster occupying 3-6 kb between the genes mry and scpA on the chromosome of Streptococcus pyogenes. Most GAS strains contain one to three tandemly arranged copies of emm-family genes in the cluster, but the alleles within the cluster vary among different strains. Phylogenetic analysis of the conserved sequences at the 3' end of these genes differentiates all known members of this family into four evolutionarily distinct emm subfamilies. As a starting point to analyze how the different subfamilies are related evolutionarily, the structure of the emm chromosomal region was mapped in a number of diverse GAS strains by using subfamily-specific primers in the polymerase chain reaction. Nine distinct chromosomal patterns of the genes in the emm gene cluster were found. These nine chromosomal patterns support a model for the evolution of the emm gene family in which gene duplication followed by sequence divergence resulted in the generation of four major-gene subfamilies in this locus.
emm基因是A群链球菌（GAS）中一个基因家族的成员，该家族编码抗吞噬细胞表面蛋白和/或免疫球蛋白结合蛋白。此前该家族中已测序的基因被命名为“emm”“fcrA”“enn”“arp”“protH”和“mrp”；在此将它们统称为“emm基因家族”。emm家族的基因位于化脓性链球菌染色体上mry和scpA基因之间一个长3至6 kb的簇中。大多数GAS菌株在该簇中含有一至三个串联排列的emm家族基因拷贝，但不同菌株中该簇内的等位基因有所不同。对这些基因3'端保守序列的系统发育分析将该家族所有已知成员分为四个进化上不同的emm亚家族。作为分析不同亚家族如何在进化上相关的起点，通过在聚合酶链反应中使用亚家族特异性引物，在多种不同的GAS菌株中绘制了emm染色体区域的结构。发现了emm基因簇中基因的九种不同染色体模式。这九种染色体模式支持了emm基因家族进化的一个模型，即基因复制后接着序列分歧导致了该位点四个主要基因亚家族的产生。
