The human U1 snRNA is encoded by a multigene family consisting of transcribed variants and defective pseudogenes. Many variant U1 (vU1) snRNAs have been demonstrated to not only be transcribed but also processed by the addition of a trimethylated guanosine cap, packaged into snRNPs, and assembled into spliceosomes; however, their capacity to facilitate pre-mRNA splicing has, so far, not been tested. A recent systematic analysis of the human snRNA genes identified 178 U1 snRNA genes that are present in the genome as either tandem arrays or single genes on multiple chromosomes. Of these, 15 were found to be expressed in human tissues and cell lines, although at significantly low levels from their endogenous loci, <0.001% of the canonical U1 snRNA. In this study, we found that placing the variants in the context of the regulatory elements of the RNU1-1 gene improves the expression of many variants to levels comparable to the canonical U1 snRNA. Application of a previously established HeLa cell-based minigene reporter assay to examine the capacity of the vU1 snRNAs to support pre-mRNA splicing revealed that even though the exogenously expressed variant snRNAs were enriched in the nucleus, only a few had a measurable effect on splicing.

中文翻译：

---

检查人类 U1 snRNA 变体促进前 mRNA 剪接的能力

人类 U1 snRNA 由转录变体和有缺陷的假基因组成的多基因家族编码。许多 U1 (vU1) snRNA 变体已被证明不仅可以转录，还可以通过添加三甲基化鸟苷帽进行加工，包装成 snRNP，并组装成剪接体；然而，迄今为止，它们促进前 mRNA 剪接的能力尚未经过测试。最近对人类 snRNA 基因的系统分析发现了 178 个 U1 snRNA 基因，它们以串联阵列或多条染色体上的单个基因的形式存在于基因组中。其中，15 个被发现在人体组织和细胞系中表达，尽管其内源基因座的水平显着较低，< 规范 U1 snRNA 的 0.001%。在这项研究中，我们发现将变体置于RNU1-1基因调控元件的背景下，可以将许多变体的表达提高到与经典 U1 snRNA 相当的水平。应用先前建立的基于 HeLa 细胞的小基因报告测定法来检查 vU1 snRNA 支持前 mRNA 剪接的能力，结果表明，尽管外源表达的变异 snRNA 在细胞核中富集，但只有少数对剪接具有可测量的影响。