U5 snRNP is a complex particle essential for RNA splicing. U5 snRNPs undergo intricate biogenesis that ensures that only a fully mature particle assembles into a splicing competent U4/U6•U5 tri-snRNP and enters the splicing reaction. During splicing, U5 snRNP is substantially rearranged and leaves as a U5/PRPF19 post-splicing particle, which requires re-generation before the next round of splicing. Here, we show that a previously uncharacterized protein TSSC4 is a component of U5 snRNP that promotes tri-snRNP formation. We provide evidence that TSSC4 associates with U5 snRNP chaperones, U5 snRNP and the U5/PRPF19 particle. Specifically, TSSC4 interacts with U5-specific proteins PRPF8, EFTUD2 and SNRNP200. We also identified TSSC4 domains critical for the interaction with U5 snRNP and the PRPF19 complex, as well as for TSSC4 function in tri-snRNP assembly. TSSC4 emerges as a specific chaperone that acts in U5 snRNP de novo biogenesis as well as post-splicing recycling.

• MeSH
• Down-Regulation MeSH
• Peptide Elongation Factors MeSH
• DNA Repair Enzymes metabolism   MeSH
• HeLa Cells MeSH
• Protein Interaction Domains and Motifs MeSH
• Nuclear Proteins metabolism   MeSH
• Humans MeSH
• Ribonucleoprotein, U5 Small Nuclear chemistry   metabolism   MeSH
• Tumor Suppressor Proteins chemistry   genetics   metabolism   MeSH
• Protein Domains MeSH
• RNA-Binding Proteins metabolism   MeSH
• Recombinant Fusion Proteins MeSH
• Ribonucleoproteins, Small Nuclear chemistry   metabolism   MeSH
• RNA Splicing MeSH
• RNA Splicing Factors metabolism   MeSH
• Spliceosomes metabolism   MeSH
• Transcription Factors MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• EFTUD2 protein, human MeSH Browser
• Peptide Elongation Factors MeSH
• DNA Repair Enzymes MeSH
• Nuclear Proteins MeSH
• Ribonucleoprotein, U5 Small Nuclear MeSH
• Tumor Suppressor Proteins MeSH
• RNA-Binding Proteins MeSH
• PRPF19 protein, human MeSH Browser
• PRPF6 protein, human MeSH Browser
• PRPF8 protein, human MeSH Browser
• Recombinant Fusion Proteins MeSH
• Ribonucleoproteins, Small Nuclear MeSH
• RNA Splicing Factors MeSH
• SNRNP200 protein, human MeSH Browser
• Transcription Factors MeSH
• TSSC4 protein, human MeSH Browser

Splicing is catalyzed by the spliceosome, a complex of five major small nuclear ribonucleoprotein particles (snRNPs). The pre-mRNA splicing factor PRPF8 is a crucial component of the U5 snRNP, and together with EFTUD2 and SNRNP200, it forms a central module of the spliceosome. Using quantitative proteomics, we identified assembly intermediates containing PRPF8, EFTUD2, and SNRNP200 in association with the HSP90/R2TP complex, its ZNHIT2 cofactor, and additional proteins. HSP90 and R2TP bind unassembled U5 proteins in the cytoplasm, stabilize them, and promote the formation of the U5 snRNP. We further found that PRPF8 mutants causing Retinitis pigmentosa assemble less efficiently with the U5 snRNP and bind more strongly to R2TP, with one mutant retained in the cytoplasm in an R2TP-dependent manner. We propose that the HSP90/R2TP chaperone system promotes the assembly of a key module of U5 snRNP while assuring the quality control of PRPF8. The proteomics data further reveal new interactions between R2TP and the tuberous sclerosis complex (TSC), pointing to a potential link between growth signals and the assembly of key cellular machines.

• MeSH
• Peptide Elongation Factors genetics   metabolism   MeSH
• HeLa Cells MeSH
• Protein Interaction Domains and Motifs MeSH
• Humans MeSH
• Ribonucleoprotein, U1 Small Nuclear metabolism   MeSH
• Ribonucleoprotein, U4-U6 Small Nuclear metabolism   MeSH
• Ribonucleoprotein, U5 Small Nuclear genetics   metabolism   MeSH
• RNA, Messenger genetics   metabolism   MeSH
• Multiprotein Complexes MeSH
• Mutation MeSH
• RNA Precursors genetics   metabolism   MeSH
• HSP90 Heat-Shock Proteins metabolism   MeSH
• RNA-Binding Proteins genetics   metabolism   MeSH
• Calcium-Binding Proteins metabolism   MeSH
• Proteomics methods   MeSH
• Retinitis Pigmentosa genetics   metabolism   MeSH
• RNA Interference MeSH
• RNA Splicing * MeSH
• Protein Stability MeSH
• Transfection MeSH
• Protein Binding MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• EFTUD2 protein, human MeSH Browser
• Peptide Elongation Factors MeSH
• Ribonucleoprotein, U1 Small Nuclear MeSH
• Ribonucleoprotein, U4-U6 Small Nuclear MeSH
• Ribonucleoprotein, U5 Small Nuclear MeSH
• RNA, Messenger MeSH
• Multiprotein Complexes MeSH
• RNA Precursors MeSH
• HSP90 Heat-Shock Proteins MeSH
• RNA-Binding Proteins MeSH
• Calcium-Binding Proteins MeSH
• PRPF8 protein, human MeSH Browser
• TESC protein, human MeSH Browser

Spliceosomal snRNPs are complex particles that proceed through a fascinating maturation pathway. Several steps of this pathway are closely linked to nuclear non-membrane structures called Cajal bodies. In this review, I summarize the last 20 y of research in this field. I primarily focus on snRNP biogenesis, specifically on the steps that involve Cajal bodies. I also evaluate the contribution of the Cajal body in snRNP quality control and discuss the role of snRNPs in Cajal body formation.

• MeSH
• Coiled Bodies metabolism   MeSH
• Transcription, Genetic MeSH
• Humans MeSH
• RNA Processing, Post-Transcriptional MeSH
• Ribonucleoproteins, Small Nuclear genetics   metabolism   MeSH
• Spliceosomes MeSH
• Protein Binding MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Ribonucleoproteins, Small Nuclear MeSH