Maki Kimika, Uno Kanako, Morita Teppei, Aiba Hiroji
Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa, Nagoya 464-8602, Japan.
Proc Natl Acad Sci U S A. 2008 Jul 29;105(30):10332-7. doi: 10.1073/pnas.0803106105. Epub 2008 Jul 23.
SgrS is an Hfq-binding small RNA that is induced under glucose phosphate stress in Escherichia coli. It forms a specific ribo nucleo protein complex with Hfq and RNase E resulting in translational repression and rapid degradation of ptsG mRNA, encoding the glucose transporter. Here, we report translational silencing of ptsG mRNA in a defined in vitro system. We demonstrate that SgrS and Hfq are the minimum components for translational silencing to faithfully reproduce the reaction in cells. We show that ptsG-SgrS base pairing is sufficient to cause translational repression when the ptsG mRNA is forced to base pair with SgrS without the help of Hfq. The extent of translational repression correlates with the extent of duplex formation. We conclude that base pairing itself but not Hfq is directly responsible for translational silencing and the major role of Hfq in gene silencing is to stimulate the base pairing between SgrS and ptsG mRNA. This simple mechanism is in striking contrast to miRNA action in eukaryote in which the RNA is believed to act only as a guide of protein partners.
SgrS是一种与Hfq结合的小RNA，在大肠杆菌的磷酸葡萄糖胁迫下被诱导产生。它与Hfq和核糖核酸酶E形成一种特定的核糖核蛋白复合物，导致编码葡萄糖转运蛋白的ptsG mRNA发生翻译抑制和快速降解。在此，我们报道了在一个明确的体外系统中ptsG mRNA的翻译沉默。我们证明，SgrS和Hfq是翻译沉默忠实再现细胞内反应的最小组成部分。我们表明，当ptsG mRNA在没有Hfq帮助的情况下被迫与SgrS碱基配对时，ptsG与SgrS的碱基配对足以导致翻译抑制。翻译抑制的程度与双链体形成的程度相关。我们得出结论，碱基配对本身而非Hfq直接导致翻译沉默，并且Hfq在基因沉默中的主要作用是刺激SgrS与ptsG mRNA之间的碱基配对。这种简单的机制与真核生物中miRNA的作用形成鲜明对比，在真核生物中，RNA被认为仅作为蛋白质伴侣的引导物发挥作用。
