mRNA rpoS编码大肠杆菌中的一般应激响应的核心蛋白Sigma因子σs，通过σs和RNA 聚合酶的相互作用，rpoS直接或间接的调控着大肠杆菌中约10%的基因的表达。rpoS 5’非编码区的核糖体结合位点位于一段自抑制茎环结构中，因此rpoS处于基因表达的非激活状态。在细菌的应激响应中，一系列的小非编码RNA在Hfq蛋白的帮助下，与rpoS发生互补配对来释放mRNA上核糖体的结合位点，从而实现对目标基因表达的上调。最新的证据显示rpoS 5’非编码区的自抑制茎环结构中的一段loop区5’-UUAUUU-3’可以与Hfq六聚体圆盘侧面发生特异性相互作用，而且对rpoS基因的表达调控非常重要。我们计划解析该自抑制茎环核心区域的空间结构，并进一步研究它与Hfq蛋白相互作用的结构基础，来了解该相互作用的是否会对自抑制茎环的结构或者稳定性产生影响，从而参与了sRNA对rpoS的基因表达调控。

The mRNA rpoS encodes the alternative sigma factor σs that mediates the expression of many stress response genes in E. coli. This response allows cells to become more resistant not only to the stress that they first encounter but also to other stressful treatments. Interacting with the core RNA polymerase, rpoS regulates 10% of the E. coli genome (approximately 500 genes) directly or indirectly. During exponential growth, translation of the rpoS mRNA is inhibited by a stable inhibitory stem-loop structure located at its 5’ untranslated region (5’-UTR) that masks the Shine-Dalgarno sequence. In stress response of E. coli, some small non-coding RNAs (sRNAs) are induced, with the help of RNA chaperon Hfq, to up-regulate rpoS translation by base pairing with the rpoS leader and opening the inhibitory stem, releasing the Shine–Dalgarno sequence for translation initiation. A recent study by Woodson et al. reported a new specific interaction between the loop region of the inhibitory stem-loop structure and the rim region of Hfq hexamer protein, and proved that this interaction is important for the expression regulation of rpoS by sRNA. In this research, we are planning to solve the 3D structure of rpoS 5’-UTR inhibitory stem-loop and further study the structural basis of its interaction with Hfq hexamer. Our aim is to learn whether the interaction with Hfq will influence the structure and/or stability of this inhibitory stem-loop and therefore contribute to the sRNA-mediated expression regulation of rpoS.