SRm160 splicing coactivator promotes transcript 3′-end cleavage
SRm160 splicing coactivator promotes transcript 3′-end cleavage
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DOI：
10.1128/mcb.22.1.148-160.2002
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发表时间：
2002-01-01
影响因子：
5.3
通讯作者：
Blencowe, BJ
中科院分区：
文献类型：
--
作者：
McCracken, S;Lambermon, M;Blencowe, BJ
前体mRNA加工的各个步骤，包括5'端帽子形成、剪接以及3'端加工（切割和多聚腺苷酸化）是高度整合的，并且能够相互影响。此外，前期的剪接能够影响基因表达的下游步骤，包括mRNA从细胞核的输出。然而，协调前体mRNA转录本成熟过程中这些步骤的因子和机制尚未被充分了解。在本研究中，我们证明了SRm160（一种160kDa的丝氨酸/精氨酸重复相关核基质蛋白），一种组成型和外显子增强子依赖型剪接的共激活因子，参与了3'端形成。SRm160水平的升高在体内和体外都促进了转录本的3'端切割。值得注意的是，在体内高水平的SRm160激活了未剪接的前体mRNA的3'端切割和细胞质积累，从而使促进这些转录本3'端形成和核释放所需的剪接要求解偶联。与在与剪接相关的3'端形成中的作用一致，发现SRm160与切割多聚腺苷酸化特异性因子特异性结合，并且在体外比无剪接活性的前体mRNA更有效地刺激有剪接活性的前体mRNA的3'端切割。这些结果为SRm160在mRNA 3'端形成中的作用提供了证据，并表明这种剪接共激活因子的水平对于前体mRNA加工事件的恰当协调是重要的。
Individual steps in the processing of pre-mRNA, including 5'-end cap formation, splicing, and 3'-end processing (cleavage and polyadenylation) are highly integrated and can influence one another. In addition, prior splicing can influence downstream steps in gene expression, including export of mRNA from the nucleus. However, the factors and mechanisms coordinating these steps in the maturation of pre-mRNA transcripts are not well understood. In the present study we demonstrate that SRm160 (for serine/arginine repeat-related nuclear matrix protein of 160 kDa), a coactivator of constitutive and exon enhancer-dependent splicing, participates in X-end formation. Increased levels of SRm160 promoted the 3'-end cleavage of transcripts both in vivo and in vitro. Remarkably, at high levels in vivo SRm160 activated the X-end cleavage and cytoplasmic accumulation of unspliced pre-mRNAs, thereby uncoupling the requirement for splicing to promote the 3'-end formation and nuclear release of these transcripts. Consistent with a role in 3'-end formation coupled to splicing, SRm160 was found to associate specifically with the cleavage polyadenylation specificity factor and to stimulate the X-end cleavage of splicing-active pre-mRNAs more efficiently than that of splicing-inactive pre-mRNAs in vitro. The results provide evidence for a role for SRm160 in mRNA X-end formation and suggest that the level of this splicing coactivator is important for the proper coordination of pre-mRNA processing events.