Howard Hughes Medical Institute, University of Massachusetts Medical School, Worcester, MA 01605; Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605.
Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605.
Cell. 2012 Nov 9;151(4):750-764. doi: 10.1016/j.cell.2012.10.007. Epub 2012 Oct 18.
In addition to sculpting eukaryotic transcripts by removing introns, pre-mRNA splicing greatly impacts protein composition of the emerging mRNP. The exon junction complex (EJC), deposited upstream of exon-exon junctions after splicing, is a major constituent of spliced mRNPs. Here, we report comprehensive analysis of the endogenous human EJC protein and RNA interactomes. We confirm that the major "canonical" EJC occupancy site in vivo lies 24 nucleotides upstream of exon junctions and that the majority of exon junctions carry an EJC. Unexpectedly, we find that endogenous EJCs multimerize with one another and with numerous SR proteins to form megadalton sized complexes in which SR proteins are super-stoichiometric to EJC core factors. This tight physical association may explain known functional parallels between EJCs and SR proteins. Further, their protection of long mRNA stretches from nuclease digestion suggests that endogenous EJCs and SR proteins cooperate to promote mRNA packaging and compaction.
除了通过去除内含子来塑造真核转录本,前体 mRNA 的剪接还极大地影响了新生 mRNP 的蛋白质组成。剪接后在exon-exon 交界处上游沉积的外显子连接复合物 (EJC) 是剪接 mRNP 的主要成分。在这里,我们报告了对内源性人 EJC 蛋白和 RNA 相互作用组的全面分析。我们证实,体内主要的“典型”EJC 占据位点位于exon 交界处上游 24 个核苷酸处,并且大多数 exon 交界处都带有 EJC。出人意料的是,我们发现内源性 EJCs 彼此以及与许多 SR 蛋白相互多聚化,形成兆道尔顿大小的复合物,其中 SR 蛋白的数量超过 EJC 核心因子。这种紧密的物理关联可能解释了 EJCs 和 SR 蛋白之间已知的功能相似性。此外,它们保护长 mRNA 片段免受核酸酶消化表明,内源性 EJCs 和 SR 蛋白合作促进 mRNA 的包装和压缩。