Wang Pingping, Palfi Zsofia, Preusser Christian, Lücke Stephan, Lane William S, Kambach Christian, Bindereif Albrecht
Institut für Biochemie, Justus-Liebig-Universität Giessen, Giessen, Germany.
EMBO J. 2006 Oct 4;25(19):4513-23. doi: 10.1038/sj.emboj.7601328. Epub 2006 Sep 14.
Messenger RNA processing in trypanosomes by cis and trans splicing requires spliceosomal small nuclear ribonucleoproteins (snRNPs) U1, U2, U4/U6, and U5, as well as the spliced leader (SL) RNP. As in other eukaryotes, these RNPs share a core structure of seven Sm polypeptides. Here, we report that the identity of the Sm protein constituents varies between spliceosomal snRNPs: specifically, two of the canonical Sm proteins, SmB and SmD3, are replaced in the U2 snRNP by two novel, U2 snRNP-specific Sm proteins, Sm15K and Sm16.5K. We present a model for the variant Sm core in the U2 snRNP, based on tandem affinity purification-tagging and in vitro protein-protein interaction assays. Using in vitro reconstitutions with canonical and U2-specific Sm cores, we show that the exchange of two Sm subunits determines discrimination between individual Sm sites. In sum, we have demonstrated that the heteroheptameric Sm core structure varies between spliceosomal snRNPs, and that modulation of the Sm core composition mediates the recognition of small nuclear RNA-specific Sm sites.
锥虫中通过顺式和反式剪接进行的信使核糖核酸加工需要剪接体小核核糖核蛋白（snRNP）U1、U2、U4/U6和U5，以及剪接前导序列（SL）核糖核蛋白。与其他真核生物一样，这些核糖核蛋白具有由七种Sm多肽组成的核心结构。在此，我们报道剪接体snRNP之间Sm蛋白成分的身份有所不同：具体而言，U2 snRNP中的两种典型Sm蛋白SmB和SmD3被两种新的、U2 snRNP特异性的Sm蛋白Sm15K和Sm16.5K所取代。基于串联亲和纯化标记和体外蛋白质-蛋白质相互作用分析，我们提出了U2 snRNP中变体Sm核心的模型。通过使用典型和U2特异性Sm核心进行体外重组，我们表明两个Sm亚基的交换决定了对各个Sm位点的区分。总之，我们已经证明异源七聚体Sm核心结构在剪接体snRNP之间有所不同，并且Sm核心组成的调节介导了对小核RNA特异性Sm位点的识别。
