Unique Sm core structure of U7 snRNPs:: assembly by a specialized SMN complex and the role of a new component, Lsm11, in histone RNA processing
Unique Sm core structure of U7 snRNPs:: assembly by a specialized SMN complex and the role of a new component, Lsm11, in histone RNA processing
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DOI：
10.1101/gad.274403
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发表时间：
2003-09-15
影响因子：
10.5
通讯作者：
Schümperli, D
中科院分区：
文献类型：
--
作者：
Pillai, RS;Grimmler, M;Schümperli, D
一组七个Sm蛋白组装在Sm-结合位点的剪接体U snRNAs，形成环形Sm核心。参与组蛋白RNA 3'加工的U 7 snRNP含有结构相似但生物化学独特的Sm核心，其中两种蛋白质Sm D1和D2被Lsm 10和另一种未知组分取代。在这里，我们的特点是这个因素，称为Lsm 11，作为一种新的Sm样蛋白，显然有两个不同的功能。体外研究表明，其长的N-末端部分介导了组蛋白mRNA 3 '端切割的重要步骤，最有可能是通过招募先前被鉴定为加工因子的锌指蛋白。相反，C-末端部分，其中包括两个Sm基序中断了一个非常长的间隔，是足以组装U 7，但不是U1，snRNA。这种U 7特异性Sm核心的组装取决于U 7 snRNA的非经典Sm结合位点。此外，它是由一个专门的SMN复合物，含有Lsm 10和Lsm 11，但缺乏Sm D1/D2促进。因此，U 7特异性Lsm 11蛋白不仅指定了U 7 Sm核心的组装，而且在U 7 snRNP介导的组蛋白mRNA加工中发挥重要作用。
A set of seven Sm proteins assemble on the Sm-binding site of spliceosomal U snRNAs to form the ring-shaped Sm core. The U7 snRNP involved in histone RNA 3' processing contains a structurally similar but biochemically unique Sm core in which two of these proteins, Sm D1 and D2, are replaced by Lsm10 and by another as yet unknown component. Here we characterize this factor, termed Lsm11, as a novel Sm-like protein with apparently two distinct functions. In vitro studies suggest that its long N-terminal part mediates an important step in histone mRNA 3'-end cleavage, most likely by recruiting a zinc finger protein previously identified as a processing factor. In contrast, the C-terminal part, which comprises two Sm motifs interrupted by an unusually long spacer, is sufficient to assemble with U7, but not U1, snRNA. Assembly of this U7-specific Sm core depends on the noncanonical Sm-binding site of U7 snRNA. Moreover, it is facilitated by a specialized SMN complex that contains Lsm10 and Lsm11 but lacks Sm D1/D2. Thus, the U7-specific Lsm11 protein not only specifies the assembly of the U7 Sm core but also fulfills an important role in U7 snRNP-mediated histone mRNA processing.