ISOLATION OF SACCHAROMYCES-CEREVISIAE SNRNPS - COMPARISON OF U1 AND U4 U6.U5 TO THEIR HUMAN COUNTERPARTS/

Small nuclear ribonucleoprotein (snRNP) particles are essential for pr e-messenger RNA splicing. In human HeLa cells, 40 proteins associated with snRNPs have been identified. Yet, the function of many of these p roteins remains unknown. Here, the immunoaffinity purification of the spliceosomal snRNPs U1, U2, U4/U6.U5, and several nucleolar snRNP spec ies from the yeast Saccharomyces cerevisiae is presented. The U1 and U 4/U6.U5 snRNPs were purified extensively and their protein composition and ultrastructure analyzed. The yeast U1 snRNP is larger and contain s three times more specific proteins than its human counterpart. In co ntrast, the size, protein composition, and morphology of the yeast and the human U4/U6.U5 snRNPs are significantly similar. The preparative isolation of yeast snRNPs will allow the cloning as well as genetic an d phylogenetic analysis of snRNP proteins which will accelerate our un derstanding of their function.