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首页> 外文期刊>Infection and immunity >Phylogenetic distribution of streptococcal superantigen SSA allelic variants provides evidence for horizontal transfer of ssa within Streptococcus pyogenes.
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Phylogenetic distribution of streptococcal superantigen SSA allelic variants provides evidence for horizontal transfer of ssa within Streptococcus pyogenes.

机译：链球菌超抗原SSA等位基因变体的系统发育分布提供了SSA水平转移的证据，SSA在链球菌中的细胞活性。

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Phylogenetic analyses recently found the gene encoding the streptococcal superantigen SSA of Streptococcus pyogenes to occur in several well-differentiated clones comprising 10 (12.5%) of 80 clonal lineages examined. To determine if distinct clonal lineages carried the same ssa coding sequence or harbored a group of allelic variants, ssa was sequenced from 23 S. pyogenes strains representing the 10 clones identified by multilocus enzyme electrophoresis. Three alleles of ssa were found in natural populations of S. pyogenes. ssa-1 and ssa-3 differed by a single synonymous substitution in codon 94; both encoded SSA-1. Each of these alleles was present in phylogenetically diverse clones that had not shared a recent common ancestor. ssa-2 was present in a single clonal lineage. It was identical to ssa-3 at codon 94 but had a nonsynonymous substitution at codon 28 that changed the second amino acid of the mature protein from serine to arginine. This substitution altered the predicted isoelectric point and affected the apparent molecular mass during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Despite sequence variation both upstream of and within the ssa locus, all ssa-positive lineages expressed either SSA-1 or SSA-2. The observed patterns of ssa allele-clone distribution provide evidence for individual incidences of horizontal transfer and recombination of ssa among distinct group A streptococcal lineages. Although the extensive homology of SSA to the staphylococcal superantigen SEB raises the possibility of intergeneric gene transfer, a search for ssa in 68 genetically diverse clones of Staphylococcus aureus did not identify the gene. Moreover, the absence of ssa among 119 representative strains of Lancefield group B, C, or G streptococci suggests that ssa is confined to S. pyogenes.
机译：系统发育分析最近发现编码链球菌化脓性的链球菌超羊膜SSA的基因在几种良好分化的克隆中发生，所述克隆的几种良好分化的克隆，所述80个克隆谱系检测。为了确定不同的克隆谱系是否携带相同的SSA编码序列或覆盖一组等位基因变体，从代表通过多层酶电泳鉴定的10个克隆的23秒菌株测序SSA。 SSA的三位等位基因在S. pyogeneses的天然群体中发现。 SSA-1和SSA-3在密码子94中的单一同义替换不同;两个编码的SSA-1。这些等位基因中的每一个存在于系统源性多样的克隆中，这些克隆并未分享最近的共同祖先。 SSA-2以单个克隆谱系存在。它在密码子94处与SSA-3相同，但在密码子28处具有不同族替代，其将成熟蛋白的第二氨基酸从丝氨酸改变为精氨酸。该取代改变了预测的等电点，并影响了十二烷基硫酸钠 - 聚丙烯酰胺凝胶电泳期间表观分子量。尽管SSA基因座的上游和在SSA基因座内部的序列变化，但所有SSA正谱系都表达了SSA-1或SSA-2。观察到的SSA等位基因 - 克隆分布模式为不同的组中SSA水平转移和重组的单独发病提供了证据，该综合组是一种链球菌谱系。尽管SSA对葡萄球菌超抗原SEB的广泛同源性引发了代苯基基因转移的可能性，但是在68个遗传上不同克隆金黄色葡萄球菌的SSA搜索没有识别该基因。此外，在119个代表性菌株B，C或G链球菌的119个代表性菌株中没有SSA的情况表明SSA限制在Pyogenes中。

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