蛋白质精氨酸甲基化发生在剪接体成分和剪接体相关蛋白上,但是这种修饰如何有助于它们在前mRNA剪接中的功能仍然很少。在这里,我们提供证据表明,酵母SR-/hnRNP样蛋白Npl3的蛋白质精氨酸甲基化在促进SUS1内含子的有效剪接中起作用,该内含子具有非共有5'剪接位点和分支位点。在缺乏主要蛋白质精氨酸甲基转移酶HMT1的酵母细胞中,我们观察到U1snRNP亚基Snp1和Npl3的共转录募集到具有共识(ECM33和ASC1)和非共识(SUS1)5'剪接位点和分支位点的前mRNA的变化。使用在Δhmt1细胞中表达时表型野生型Npl3的Npl3突变体,我们发现Npl3的精氨酸甲基化是造成这种情况的原因。对这些突变体中前mRNA剪接效率的检查表明,SUS1内含子1的有效剪接需要Npl3甲基化,而ECM33或ASC1则不需要。将SUS1内含子1中的5'剪接位点和分支位点改变为共识以Hmt1-非依赖性方式形成恢复的剪接效率。生化研究的结果表明,Npl3的甲基化通过与U1snRNP亚基Mud1的关联来促进其与U1snRNP的最佳关联。基于这些数据,我们提出了一个模型,其中Hmt1通过Npl3的精氨酸甲基化,促进U1snRNP与pre-mRNA的接合,以促进剪接机制对非共有剪接位点的利用.
Protein arginine methylation occurs on spliceosomal components and spliceosome-associated proteins, but how this modification contributes to their function in pre-mRNA splicing remains sparse. Here we provide evidence that protein arginine methylation of the yeast SR-/hnRNP-like protein Npl3 plays a role in facilitating efficient splicing of the SUS1 intron that harbors a non-
consensus 5\' splice site and branch site. In yeast cells lacking the major protein arginine methyltransferase HMT1, we observed a change in the co-transcriptional recruitment of the U1 snRNP subunit Snp1 and Npl3 to pre-mRNAs harboring both
consensus (ECM33 and ASC1) and non-
consensus (SUS1) 5\' splice site and branch site. Using an Npl3 mutant that phenocopies wild-type Npl3 when expressed in Δhmt1 cells, we showed that the arginine methylation of Npl3 is responsible for this. Examination of pre-mRNA splicing efficiency in these mutants reveals the requirement of Npl3 methylation for the efficient splicing of SUS1 intron 1, but not of ECM33 or ASC1. Changing the 5\' splice site and branch site in SUS1 intron 1 to the
consensus form restored splicing efficiency in an Hmt1-independent manner. Results from biochemical studies show that methylation of Npl3 promotes its optimal association with the U1 snRNP through its association with the U1 snRNP subunit Mud1. Based on these data, we propose a model in which Hmt1, via arginine methylation of Npl3, facilitates U1 snRNP engagement with the pre-mRNA to promote usage of non-
consensus splice sites by the splicing machinery.