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首页> 外文期刊>Journal of bacteriology >A Family of Transcriptional Antitermination Factors Necessary for Synthesis of the Capsular Polysaccharides of Bacteroides fragilis
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A Family of Transcriptional Antitermination Factors Necessary for Synthesis of the Capsular Polysaccharides of Bacteroides fragilis

机译：脆弱拟杆菌的荚膜多糖合成所需的转录抗终止因子家族。

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A single strain of Bacteroides fragilis synthesizes eight distinct capsular polysaccharides, designated PSA to PSH. These polysaccharides are synthesized by-products encoded by eight separate polysaccharide biosynthesis loci. The genetic architecture of each of these eight loci is similar, including the fact that the first gene of each locus is a paralog of the first gene of each of the other PS loci. These proteins are designated the UpxY family, where x is replaced by a to h, depending upon the polysaccharide locus from which it is produced. Mutational analysis of three separate upxY genes demonstrated that they are necessary and specific for transcription of their respective polysaccharide biosynthesis operon and that they function in trans. Transcriptional reporter constructs, reverse transcriptase PCR, and deletion analysis demonstrated that the UpxYs do not affect initiation of transcription, but rather prevent premature transcriptional termination within the 5′ untranslated region between the promoter and the upxY gene. The UpxYs have conserved motifs that are present in NusG and NusG-like proteins. Mutation of two conserved residues within the conserved KOW motif abrogated UpaY activity, further confirming that these proteins belong to the NusG-like (NusGSP) family. Alignment of highly similar UpxYs led to the identification of a small region of these proteins predicted to confer specificity for their respective loci. Construction of an upaY-upeY hybrid that produced a protein in which a 17-amino-acid segment of UpaY was changed to that of UpeY altered UpaY's specificity, as it was now able to function in transcriptional antitermination of the PSE biosynthesis operon.
机译：单一的脆弱拟杆菌菌株可合成8种不同的荚膜多糖，称为PSA至PSH。这些多糖是由八个单独的多糖生物合成基因座编码的副产物。这八个基因座中每个基因座的遗传结构都是相似的，包括每个基因座的第一个基因是另一个PS基因座的第一个基因的旁系同源物。这些蛋白质被命名为UpxY家族，其中x被a替换为h，这取决于产生蛋白质的多糖基因座。对三个独立的 upxY 基因进行突变分析表明，它们对于各自的多糖生物合成操纵子的转录是必需的和特异性的，并且它们在 trans 中起作用。转录报告基因构建，逆转录酶PCR和缺失分析表明，UpxYs不影响转录的起始，而是阻止启动子和 upxY 基因之间5'非翻译区内的过早转录终止。 UpxY具有在NusG和类似NusG的蛋白质中存在的保守基序。保守的KOW基序内两个保守残基的突变消除了UpaY活性，进一步证实了这些蛋白属于NusG样（NusG SP ）家族。高度相似的UpxY的比对导致鉴定了这些蛋白的一小部分区域，这些区域预计将为其各自的基因座提供特异性。构建 upaY-upeY 杂种，该杂种产生一种蛋白质，其中UpaY的17个氨基酸区段变为UpeY的区段改变了UpaY的特异性，因为它现在能够在转录抗终止中发挥作用PSE生物合成操纵子。

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