Wolf Tinka, Janzen Wiebke, Blum Corinna, Schnetz Karin
Institut für Genetik, Universität zu Köln, Zülpicher Str. 47, 50674 Cologne, Germany.
J Bacteriol. 2006 Oct;188(19):6728-38. doi: 10.1128/JB.00586-06.
StpA has functional similarity to its homologue, the nucleoid structuring protein H-NS. It binds to AT-rich, planar, bent DNA and constrains DNA supercoils. In addition, StpA acts as an RNA chaperone. StpA and H-NS also form heterodimers. However, cellular levels of StpA are low due to repression of stpA by H-NS and negative autoregulation. Here we show that effective (30-fold) repression of stpA transcription requires a downstream regulator element located within the stpA coding region. In addition, we show that StpA represses stpA threefold in an hns null mutant. In contrast, repression of the bgl operon, another H-NS-repressed system, is not achieved by StpA alone. It becomes StpA dependent in the presence of a fusion protein encompassing the N-terminal 37 amino acids of H-NS, which comprise the core of the dimerization domain. StpA also effectively complements H-NS-I119T, a mutant defective in specific DNA binding, in repression of the bgl operon. Thus, StpA complements H-NS proteins defective in DNA binding to repress bgl, while in autoregulation of stpA it acts autonomously, indicating a difference in the mechanisms of repression.
StpA与其同源物类核结构蛋白H-NS具有功能相似性。它能结合富含AT的、平面弯曲的DNA并限制DNA超螺旋。此外，StpA还可作为一种RNA伴侣。StpA和H-NS也能形成异源二聚体。然而，由于H-NS对stpA的抑制作用以及负向自调控，StpA的细胞水平较低。在此我们表明，对stpA转录进行有效（30倍）抑制需要位于stpA编码区内的一个下游调控元件。此外，我们还表明，在hns基因缺失突变体中，StpA能对stpA进行3倍的抑制。相比之下，对于另一个受H-NS抑制的系统——bgl操纵子，单独的StpA无法实现抑制作用。在存在包含H-NS N端37个氨基酸（构成二聚化结构域核心）的融合蛋白时，对bgl操纵子的抑制作用变为依赖StpA。在对bgl操纵子的抑制中，StpA还能有效互补在特异性DNA结合方面存在缺陷的突变体H-NS-I119T。因此，在对bgl操纵子的抑制中，StpA可互补DNA结合存在缺陷的H-NS蛋白，而在stpA的自调控中它自主发挥作用，这表明抑制机制存在差异。
