Centro de Biología Molecular Severo Ochoa, CSIC-UAM, Nicolás Cabrera 1, 28049 Madrid, Spain.
Pompeu Fabra University (UPF), 08003 Barcelona, Spain.
Nucleic Acids Res. 2018 Aug 21;46(14):7339-7353. doi: 10.1093/nar/gky361.
Gemin5 is a predominantly cytoplasmic protein that downregulates translation, beyond controlling snRNPs assembly. The C-terminal region harbors a non-canonical RNA-binding site consisting of two domains, RBS1 and RBS2, which differ in RNA-binding capacity and the ability to modulate translation. Here, we show that these domains recognize distinct RNA targets in living cells. Interestingly, the most abundant and exclusive RNA target of the RBS1 domain was Gemin5 mRNA. Biochemical and functional characterization of this target demonstrated that RBS1 polypeptide physically interacts with a predicted thermodynamically stable stem-loop upregulating mRNA translation, thereby counteracting the negative effect of Gemin5 protein on global protein synthesis. In support of this result, destabilization of the stem-loop impairs the stimulatory effect on translation. Moreover, RBS1 stimulates translation of the endogenous Gemin5 mRNA. Hence, although the RBS1 domain downregulates global translation, it positively enhances translation of RNA targets carrying thermodynamically stable secondary structure motifs. This mechanism allows fine-tuning the availability of Gemin5 to play its multiple roles in gene expression control.
Gemin5 是一种主要存在于细胞质中的蛋白质，它除了控制 snRNPs 组装外，还能下调翻译。C 末端区域含有一个非典型的 RNA 结合位点，由两个结构域 RBS1 和 RBS2 组成，它们在 RNA 结合能力和调节翻译的能力上有所不同。在这里，我们展示了这两个结构域在活细胞中识别不同的 RNA 靶标。有趣的是，RBS1 结构域最丰富和唯一的 RNA 靶标是 Gemin5 mRNA。对该靶标的生化和功能特征进行了表征，表明 RBS1 多肽与一个预测的热力学稳定茎环结构相互作用，从而增强了 mRNA 翻译，抵消了 Gemin5 蛋白对全球蛋白质合成的负效应。支持这一结果的是，该茎环结构的不稳定性会损害对翻译的刺激作用。此外，RBS1 还能刺激内源性 Gemin5 mRNA 的翻译。因此，尽管 RBS1 结构域下调了整体翻译，但它能正向增强携带热力学稳定二级结构模体的 RNA 靶标的翻译。这种机制允许精细调节 Gemin5 的可用性，以发挥其在基因表达控制中的多种作用。
