Nilsen Timothy W
Center for RNA Molecular Biology, Case Western Reserve University School of Medicine, 10900 Euclid Avenue, Cleveland, OH 44106-4973, USA.
Bioessays. 2003 Dec;25(12):1147-9. doi: 10.1002/bies.10394.
The primary transcripts, pre-mRNAs, of almost all protein-coding genes in higher eukaryotes contain multiple non-coding intervening sequences, introns, which must be precisely removed to yield translatable mRNAs. The process of intron excision, splicing, takes place in a massive ribonucleoprotein complex known as the spliceosome. Extensive studies, both genetic and biochemical, in a variety of systems have revealed that essential components of the spliceosome include five small RNAs-U1, U2, U4, U5 and U6, each of which functions as a RNA, protein complex called an snRNP (small nuclear ribonucleoprotein). In addition to snRNPs, splicing requires many non-snRNP protein factors, the exact nature and number of which has been unclear. Technical advances, including new affinity purification methods and improved mass spectrometry techniques, coupled with the completion of many genome sequences, have now permitted a number of proteomic analyses of purified spliceosomes. These studies, recently reviewed by Jurica and Moore,1 reveal that the spliceosome is composed of as many as 300 distinct proteins and five RNAs, making it among the most complex macromolecular machines known.
高等真核生物中几乎所有蛋白质编码基因的初级转录本，即前体mRNA，都包含多个非编码间隔序列，即内含子，这些内含子必须被精确切除才能产生可翻译的mRNA。内含子切除过程，即剪接，发生在一种称为剪接体的大型核糖核蛋白复合物中。在各种系统中进行的广泛的遗传学和生物化学研究表明，剪接体的基本组成成分包括五种小RNA——U1、U2、U4、U5和U6，它们各自作为一种RNA-蛋白质复合物发挥作用，这种复合物被称为小核核糖核蛋白（snRNP）。除了snRNP外，剪接还需要许多非snRNP蛋白质因子，其确切性质和数量尚不清楚。包括新的亲和纯化方法和改进的质谱技术在内的技术进步，再加上许多基因组序列的完成，现在已经允许对纯化的剪接体进行一些蛋白质组学分析。Jurica和Moore最近对这些研究进行了综述，1这些研究表明，剪接体由多达300种不同的蛋白质和五种RNA组成，使其成为已知的最复杂的大分子机器之一。
