Laboratory of Bacterial Genetics, Centre for DNA Fingerprinting and Diagnostics, Hyderabad 500 001, India.
J Bacteriol. 2011 Aug;193(15):3832-41. doi: 10.1128/JB.00220-11. Epub 2011 May 20.
Nascent transcripts in Escherichia coli that fail to be simultaneously translated are subject to a factor-dependent mechanism of termination (also termed a polarity) that involves the proteins Rho and NusG. In this study, we found that overexpression of YdgT suppressed the polarity relief phenotypes and restored the efficiency of termination in rho or nusG mutants. YdgT and Hha belong to the H-NS and StpA family of proteins that repress a large number of genes in Gram-negative bacteria. Variants of H-NS defective in one or the other of its two dimerization domains, but not those defective in DNA binding alone, also conferred a similar suppression phenotype in rho and nusG mutants. YdgT overexpression was associated with derepression of proU, a prototypical H-NS-silenced locus. Polarity relief conferred by rho or nusG was unaffected in a derivative completely deficient for both H-NS and StpA, although the suppression effects of YdgT or the oligomerization-defective H-NS variants were abolished in this background. Transcription elongation rates in vivo were unaffected in any of the suppressor-bearing strains. Finally, the polarity defects of rho and nusG mutants were exacerbated by Hha and YdgT deficiency. A model is proposed that invokes a novel role for the polymeric architectural scaffold formed on DNA by H-NS and StpA independent of the gene-silencing functions of these nucleoid proteins, in modulating Rho-dependent transcription termination such that interruption of the scaffold (as obtained by expression either of the H-NS oligomerization variants or of YdgT) is associated with improved termination efficiency in the rho and nusG mutants.
在大肠杆菌中，未能同时被翻译的新生转录物会受到一种依赖因子的终止机制（也称为极性）的影响，该机制涉及 Rho 和 NusG 蛋白。在这项研究中，我们发现 YdgT 的过表达抑制了极性缓解表型，并恢复了 rho 或 nusG 突变体中的终止效率。YdgT 和 Hha 属于 H-NS 和 StpA 家族的蛋白质，它们在革兰氏阴性菌中抑制大量基因的表达。H-NS 的两种二聚化结构域中的一个或另一个发生缺陷的变体，但不是单独发生 DNA 结合缺陷的变体，也在 rho 和 nusG 突变体中赋予了类似的抑制表型。YdgT 的过表达与 proU 的去阻遏有关，proU 是一个典型的 H-NS 沉默基因座。rho 或 nusG 赋予的极性缓解在完全缺乏 H-NS 和 StpA 的衍生物中不受影响，尽管 YdgT 或寡聚化缺陷的 H-NS 变体的抑制作用在这种背景下被消除。体内转录延伸率在任何携带抑制剂的菌株中都不受影响。最后，rho 和 nusG 突变体的极性缺陷因 Hha 和 YdgT 的缺乏而加剧。提出了一个模型，该模型利用 H-NS 和 StpA 在 DNA 上形成的聚合结构支架的新作用，独立于这些核蛋白的基因沉默功能，调节 Rho 依赖的转录终止，使得支架的中断（通过表达 H-NS 寡聚化变体或 YdgT 获得）与 rho 和 nusG 突变体中的终止效率提高相关。
