Department of Molecular Biology and Genetics, Aarhus University, C.F. Møllers Allé 3, Aarhus 8000, Denmark.
Institut de Biologie de l'ENS (IBENS), Département de biologie, École normale supérieure, CNRS, INSERM, Université PSL, 75005 Paris, France.
Nucleic Acids Res. 2020 Oct 9;48(18):10413-10427. doi: 10.1093/nar/gkaa744.
The nuclear Cap-Binding Complex (CBC), consisting of Nuclear Cap-Binding Protein 1 (NCBP1) and 2 (NCBP2), associates with the nascent 5'cap of RNA polymerase II transcripts and impacts RNA fate decisions. Recently, the C17orf85 protein, also called NCBP3, was suggested to form an alternative CBC by replacing NCBP2. However, applying protein-protein interaction screening of NCBP1, 2 and 3, we find that the interaction profile of NCBP3 is distinct. Whereas NCBP1 and 2 identify known CBC interactors, NCBP3 primarily interacts with components of the Exon Junction Complex (EJC) and the TRanscription and EXport (TREX) complex. NCBP3-EJC association in vitro and in vivo requires EJC core integrity and the in vivo RNA binding profiles of EJC and NCBP3 overlap. We further show that NCBP3 competes with the RNA degradation factor ZC3H18 for binding CBC-bound transcripts, and that NCBP3 positively impacts the nuclear export of polyadenylated RNAs and the expression of large multi-exonic transcripts. Collectively, our results place NCBP3 with the EJC and TREX complexes in supporting mRNA expression.
核帽结合复合物（CBC）由核帽结合蛋白 1（NCBP1）和 2（NCBP2）组成，与 RNA 聚合酶 II 转录本的新生 5'帽结合，并影响 RNA 命运决定。最近，C17orf85 蛋白，也称为 NCBP3，被认为通过取代 NCBP2 形成替代的 CBC。然而，通过应用 NCBP1、2 和 3 的蛋白质-蛋白质相互作用筛选，我们发现 NCBP3 的相互作用谱是不同的。虽然 NCBP1 和 2 鉴定了已知的 CBC 相互作用因子，但 NCBP3 主要与外显子连接复合物（EJC）和转录和输出（TREX）复合物的成分相互作用。NCBP3-EJC 体外和体内的相互作用需要 EJC 核心完整性，并且 EJC 和 NCBP3 的体内 RNA 结合谱重叠。我们进一步表明，NCBP3 与 RNA 降解因子 ZC3H18 竞争结合 CBC 结合的转录本，并且 NCBP3 对多聚腺苷酸化 RNA 的核输出和大的多外显子转录物的表达具有积极影响。总之，我们的结果将 NCBP3 与 EJC 和 TREX 复合物置于支持 mRNA 表达的位置。
