Source:http://linkedlifedata.com/resource/umls/id/C1158740
NCI: The assembly of the spliceosome is a dynamic process that involves both small ribonucleoprotein particles (snRNPs), and non-snRNP proteins. The complete spliceosome consists of 5 snRNPs (U1, U2, U4, U5, and U6) and 50-100 non-snRNP factors. The snRNPs themselves contain a snRNA and a number of different proteins. These proteins can be subdivided into two classes, those specific to the individual snRNP, and those common to all snRNPs. The later group consists of eight polypeptides; B, B', D1, D2, D3, E, F, and G, which bind together in a tight association, and are referred to as the sm proteins. While some of the particle-specific proteins have been well studied, i.e.U1-70K or U1-A, many have only been identified by their molecular weight and have yet to be cloned. These snRNP components are recruited to the pre-mRNA in an ordered manner, and begin with the recognition of exon-intron boundaries. The 5' end of the U1 snRNP recognizes the 5' splice site of the pre-mRNA. This interaction is mediated through