The 25S [U4/U6.U5] tri-snRNP (small nuclear ribonucleoprotein) is a central unit of the nuclear pre-mRNA splicing machinery. The U4, U5 and U6 snRNAs undergo numerous rearrangements in the spliceosome, and knowledge of all of the tri-snRNP proteins is crucial to the detailed investigation of the RNA dynamics during the spliceosomal cycle. Here we characterize by mass spectrometric methods the proteins of the purified [U4/U6.U5] tri-snRNP from the yeast Saccharomyces cerevisiae. In addition to the known tri-snRNP proteins (only one, Lsm3p, eluded detection), we identified eight previously uncharacterized proteins. These include four Sm-like proteins (Lsm2p, Lsm5p, Lsm6p and Lsm7p) and four specific proteins named Snu13p, Dib1p, Snu23p and Snu66p. Snu13p comprises a putative RNA-binding domain. Interestingly, the Schizosaccharomyces pombe orthologue of Dib1p, Dim1p, was previously assigned a role in cell cycle progression. The role of Snu23p, Snu66p and, additionally, Spp381p in pre-mRNA splicing was investigated in vitro and/or in vivo. Finally, we show that both tri-snRNPs and the U2 snRNP are co-precipitated with protein A-tagged versions of Snu23p, Snu66p and Spp381p from extracts fractionated by glycerol gradient centrifugation. This suggests that these proteins, at least in part, are also present in a [U2.U4/U6.U5] tetra-snRNP complex.
|Evidence ID||Analyze ID||Interactor||Interactor Systematic Name||Interactor||Interactor Systematic Name||Type||Assay||Annotation||Action||Modification||Phenotype||Source||Reference||Note|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Gene Ontology Term||Gene Ontology Term ID||Qualifier||Aspect||Method||Evidence||Source||Assigned On||Reference||Annotation Extension|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Phenotype||Experiment Type||Experiment Type Category||Mutant Information||Strain Background||Chemical||Details||Reference|
|Evidence ID||Analyze ID||Regulator||Regulator Systematic Name||Target||Target Systematic Name||Experiment||Conditions||Strain||Source||Reference|