Azzouz Teldja N, Schumperli Daniel
Institute of Cell Biology, University of Bern, 3012 Bern, Switzerland.
RNA. 2003 Dec;9(12):1532-41. doi: 10.1261/rna.5143303.
The U7 snRNP involved in histone RNA 3' end processing is related to but biochemically distinct from spliceosomal snRNPs. In vertebrates, the Sm core structure assembling around the noncanonical Sm-binding sequence of U7 snRNA contains only five of the seven standard Sm proteins. The missing Sm D1 and D2 subunits are replaced by U7-specific Sm-like proteins Lsm10 and Lsm11, at least the latter of which is important for histone RNA processing. So far, it was unknown if this special U7 snRNP composition is conserved in invertebrates. Here we describe several putative invertebrate Lsm10 and Lsm11 orthologs that display low but clear sequence similarity to their vertebrate counterparts. Immunoprecipitation studies in Drosophila S2 cells indicate that the Drosophila Lsm10 and Lsm11 orthologs (dLsm10 and dLsm11) associate with each other and with Sm B, but not with Sm D1 and D2. Moreover, dLsm11 associates with the recently characterized Drosophila U7 snRNA and, indirectly, with histone H3 pre-mRNA. Furthermore, dLsm10 and dLsm11 can assemble into U7 snRNPs in mammalian cells. These experiments demonstrate a strong evolutionary conservation of the unique U7 snRNP composition, despite a high degree of primary sequence divergence of its constituents. Therefore, Drosophila appears to be a suitable system for further genetic studies of the cell biology of U7 snRNPs.
参与组蛋白RNA 3'端加工的U7小核核糖核蛋白颗粒(snRNP)与剪接体snRNP相关,但在生化性质上有所不同。在脊椎动物中,围绕U7 snRNA的非经典Sm结合序列组装的Sm核心结构仅包含七种标准Sm蛋白中的五种。缺失的Sm D1和D2亚基被U7特异性Sm样蛋白Lsm10和Lsm11取代,其中至少后者对组蛋白RNA加工很重要。到目前为止,尚不清楚这种特殊的U7 snRNP组成在无脊椎动物中是否保守。在这里,我们描述了几种推定的无脊椎动物Lsm10和Lsm11直系同源物,它们与其脊椎动物对应物显示出低但明显的序列相似性。在果蝇S2细胞中的免疫沉淀研究表明,果蝇Lsm10和Lsm11直系同源物(dLsm10和dLsm11)相互结合并与Sm B结合,但不与Sm D1和D2结合。此外,dLsm11与最近鉴定的果蝇U7 snRNA结合,并间接与组蛋白H3前体mRNA结合。此外,dLsm10和dLsm11可以在哺乳动物细胞中组装成U7 snRNP。这些实验表明,尽管其成分的一级序列存在高度差异,但独特的U7 snRNP组成具有很强的进化保守性。因此,果蝇似乎是进一步对U7 snRNP细胞生物学进行遗传学研究的合适系统。