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SMNrp is an essential pre-mRNA splicing factor required for the formation of the mature spliceosome
G Meister1, S Hannus, O Plöttner
1Max-Planck Institute of Biochemistry, Am Klopferspitz 18a, D-82152 Martinsried, University of Göttingen, Biochemie II, Herrmann Düker Weg 12, D-37073 Göttingen, Germany.
Abstract:
SMNrp, also termed SPF30, has recently been identified in spliceosomes assembled in vitro. We have functionally characterized this protein and show that it is an essential splicing factor. We show that SMNrp is a 17S U2 snRNP-associated protein that appears in the pre-spliceosome (complex A) and the mature spliceosome (complex B) during splicing. Immunodepletion of SMNrp from nuclear extract inhibits the first step of pre-mRNA splicing by preventing the formation of complex B. Re-addition of recombinant SMNrp to immunodepleted extract reconstitutes both spliceosome formation and splicing. Mutations in two domains of SMNrp, although similarly deleterious for splicing, differed in their consequences on U2 snRNP binding, suggesting that SMNrp may also engage in interactions with splicing factors other than the U2 snRNP. In agreement with this, we present evidence for an additional interaction between SMNrp and the [U4/U6.U5] tri-snRNP. A candidate that may mediate this interaction, namely the U4/U6-90 kDa protein, has been identified. We suggest that SMNrp, as a U2 snRNP-associated protein, facilitates the recruitment of the [U4/U6.U5] tri-snRNP to the pre-spliceosome.
Insights
SMNrp (SPF30) is an essential splicing factor. This protein facilitates spliceosome formation by aiding the recruitment of key components, ensuring accurate pre-mRNA splicing.
Area of Science:
- Molecular Biology
- RNA Splicing
- Protein Function
Background:
- The spliceosome is a dynamic molecular machine responsible for pre-mRNA splicing.
- Identifying essential protein factors is crucial for understanding spliceosome assembly and function.
Purpose of the Study:
- To functionally characterize SMNrp (SPF30) as a splicing factor.
- To elucidate the role of SMNrp in spliceosome assembly and its interactions with snRNPs.
Main Methods:
- Immunodepletion and re-addition assays using nuclear extracts.
- Analysis of spliceosome complex formation (A and B).
- Mutational analysis of SMNrp domains and assessment of U2 snRNP binding.
Main Results:
- SMNrp is a 17S U2 snRNP-associated protein found in pre-spliceosomes and mature spliceosomes.
- Depletion of SMNrp inhibits spliceosome formation (Complex B) and pre-mRNA splicing.
- SMNrp interacts with both U2 snRNP and the [U4/U6.U5] tri-snRNP, potentially via the U4/U6-90 kDa protein.
Conclusions:
- SMNrp is essential for the first step of splicing, specifically for the formation of Complex B.
- SMNrp acts as a bridge, facilitating the recruitment of the [U4/U6.U5] tri-snRNP to the pre-spliceosome.
- SMNrp's interactions suggest a multifaceted role in spliceosome assembly beyond U2 snRNP association.