Molecular dissection of the assembly pathway of spliceosomal U snRNPs

剪接体snRNP的组装，虽然在体外自发的，最近已被证明是依赖于在体内的大分子蛋白质复合物的援助。这种复合物以SMN命名，SMN是神经肌肉疾病脊髓性肌萎缩症中受影响的蛋白质，它促进了snRNP在ATP依赖性反应中的细胞质组装。在这个过程中，剪接体Sm蛋白，它构成了U snRNP的蛋白质核心，必须结合到SMN复合物之前，他们转移到U snRNA。第二个复合物，其甲基转移酶PRMT 5后命名，功能调节SMN复合物。PRMT 5-复合物催化Sm蛋白B/B '、D1和D3中丝氨酸的对称二甲基化，从而增加它们对SMN-复合物的亲和力。该项目旨在更好地理解组装反应的机制，并阐明在此过程中单个复杂组件的功能。这些研究的先决条件最近已经完成，通过在体外系统，recapitulates U snRNP组装和通过生成突变SMN复合物的开发。此外，RNA干扰研究将进行测试的假设，SMN/PRMT 5-系统可能不仅作为一个组装因子，而且作为一个伴侣蛋白防止聚集的Sm蛋白和/或错误组装到非snRNA的目标。最后，我们将讨论其他RNP的形成是否需要类似于SMN/PRMT 5系统的辅助因素。

The assembly of spliceosomal snRNPs, albeit spontaneous in vitro, has recently been shown to depend on the aid of a macromolecular protein complex in vivo. This complex, named after SMN, the protein affected in the neuromuscular disease spinal muscular atrophy, facilitates the cytoplasmic assembly of snRNPs in an ATP-dependent reaction. In this process, spliceosomal Sm proteins, which constitute the protein core of U snRNPs, must bind to the SMN-complex prior to their transfer onto the U snRNA. A second com plex, termed after its methyltransferase PRMT5, functionally regulates the SMN-complex. The PRMT5-complex catalyses the symmetric dimethlyation of arginines in Sm proteins B/B', D1 and D3, thereby increasing their affinity for the SMN-complex. This project is designed to provide a better understanding of the mechanism of the assembly reaction, and to elucidate functions of individual complex components during this process. A prerequisite for these studies has recently been accomplished through the developme nt of an in-vitro-system that recapitulates U snRNP-assembly and through the generation of mutant SMN-complexes. In addition, RNA-interference studies will be conducted to test the hypothesis that the SMN/PRMT5-system may not only act as an assembly factor, but also as a chaperone preventing aggregation of Sm proteins and/or misassembly to non-snRNA targets. Finally, we will address whether the formation of other RNPs requires assisting factors akin to the SMN/PRMT5 system.