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首页> 外文学位 >The genetics, regulation and biosynthesis of group 1 capsules in Escherichia coli and Klebsiella pneumoniae.
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The genetics, regulation and biosynthesis of group 1 capsules in Escherichia coli and Klebsiella pneumoniae.

机译：大肠杆菌和肺炎克雷伯菌第1组胶囊的遗传，调控和生物合成。

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摘要

Group 1 capsules of Escherichia coli and Klebsiella pneumoniae are important virulence determinants. However, despite their importance, we still do not have a complete understanding of their biosynthetic mechanisms, transcriptional organization or regulation. The K30 capsule gene cluster (cps) from E. coli isolate E69 has been sequenced and serves as the prototype. Genes involved in high-level polymerization and surface assembly of the polymer are located promoter proximal in the cluster, while those responsible for repeat unit synthesis and polymerization are promoter distal in the cluster. In this work, the cps clusters from E. coli and K. pneumoniae isolates representing different serotypes were shown to be highly conserved in gene order and in nucleotide sequence of the serotype-independent genes. Many cps clusters are flanked upstream by partial IS elements that are implicated in genetic exchange and could explain this high degree of conservation. The first open reading frame of the clusters, orfX, is also highly conserved. Although OrfX has no homologues outside of the cps clusters, mutagenesis showed that it functions in capsule biosynthesis. OrfX was localized to the outer membrane where it is proposed to function in surface assembly.; cps transcription was shown to be driven by a region that includes an ops (o&barbelow;peron p&barbelow;olarity s&barbelow;uppressor) element, which functions in conjunction with the antitermination protein RfaH. A stem-loop structure, whose termination activity was verified in vivo, separates the serotype-independent genes from the serotype-specific genes in the K30 operon. As no promoter exists downstream of the terminator, it must function as an attenuator. A rfaH mutation resulted in decreased cps transcription.; Chromosomal fusion experiments showed that cps transcription is not directly regulated by the Rcs (r&barbelow;egulator of c&barbelow;apsule s&barbelow;ynthesis) two-component regulatory system as previously believed. Overexpression of the transcriptional activator RcsB results in a mucoid phenotype, but neither overexpression nor inactivation of RcsB affected cps transcription. High-level RcsB expression increased transcription of galF, which is involved in precursor biosynthesis. GalF overexpression results in increased K30 production without affecting cps transcription. These results suggest that levels of group 1 capsule production may be controlled in a novel manner via activation of galF.
机译：第1组大肠杆菌和肺炎克雷伯菌胶囊是重要的毒力决定因素。但是，尽管它们很重要，但我们仍然对其生物合成机制，转录组织或调控没有完全的了解。来自 E的K30胶囊基因簇（ cps ）。大肠埃希菌分离株E69已被测序，并作为原型。涉及聚合物的高级聚合和表面组装的基因位于簇的近端启动子，而负责重复单元合成和聚合的基因则位于簇的远端启动子。在这项工作中， cps 来自大肠杆菌和 K。结果表明，代表不同血清型的肺炎分离株在与血清型无关的基因的基因顺序和核苷酸序列中高度保守。许多 cps 簇的上游是部分IS元件，这些元件与基因交换有关，可以解释这种高度的保守性。簇的第一个开放阅读框， orfX ，也是高度保守的。尽管OrfX在 cps 簇之外没有同源物，但诱变表明它在胶囊生物合成中起作用。 OrfX被定位在外膜上，建议在表面组装中起作用。显示 cps 转录受包含 ops （o＆barbelow; peron p＆barbelow; olarity s＆barbelow; uppressor）元件的区域驱动，该区域与抗终止蛋白RfaH结合起作用。一种茎环结构，其终止活性在体内得到了验证，它在K30操纵子中将血清型独立基因与血清型特异性基因分开。由于终止子下游不存在启动子，因此它必须充当衰减器。 rfaH 突变导致 cps 转录降低。染色体融合实验表明， cps 转录不受先前认为的Rcs（r＆barbeeg; apulator s＆barbelow;合成的调节剂）的直接调控。转录激活因子RcsB的过表达导致粘液表型，但RcsB的过表达或失活都不会影响 cps 转录。 RcsB的高水平表达增加了 galF 的转录，这与前体的生物合成有关。 GalF的过表达导致K30产量增加，而不影响 cps 转录。这些结果表明，可以通过激活 galF 以新颖的方式控制第1组胶囊的产生水平。

著录项

  • 作者

    Rahn, Andrea Rae.;

  • 作者单位

    University of Guelph (Canada).;

  • 授予单位 University of Guelph (Canada).;
  • 学科 Biology Microbiology.; Biology Genetics.
  • 学位 Ph.D.
  • 年度 2002
  • 页码 p.4042
  • 总页数 226
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 微生物学;
  • 关键词

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