SIPP1, a novel pre-mRNA splicing factor and interactor of protein phosphatase-1.

We have identified a polypeptide that was already known to interact with polyglutamine-tract-binding protein (PQBP)-1/Npw38 as a novel splicing factor and interactor of protein phosphatase-1, hence the name SIPP1 for splicing factor that interacts with PQBP-1 and PP1 (protein phosphotase 1). SIPP1 was inhibitory to PP1, and its inhibitory potency ...
was increased by phosphorylation with protein kinase CK1. Two-hybrid and co-sedimentation analysis revealed that SIPP1 has two distinct PP1-binding domains and that the binding of SIPP1 with PP1 involves a RVXF (Arg-Val-Xaa-Phe) motif, which functions as a PP1-binding sequence in most interactors of PP1. Enhanced-green-fluorescent-protein-tagged SIPP1 was targeted exclusively to the nucleus and was enriched in the nuclear speckles, which represent storage/assembly sites of splicing factors. We have mapped a nuclear localization signal in the N-terminus of SIPP1, while the proline-rich C-terminal domain appeared to be required for its subnuclear targeting to the speckles. Finally, we found that SIPP1 is also a component of the spliceosomes and that a SIPP1-fragment inhibits splicing catalysis by nuclear extracts independent of its ability to interact with PP1.
Mesh Terms:
Amino Acid Motifs, Amino Acid Sequence, Animals, Binding Sites, COS Cells, Cell Line, Cercopithecus aethiops, Hela Cells, Humans, Mice, Molecular Sequence Data, Phosphoprotein Phosphatases, Protein Phosphatase 1, Proteins, RNA Precursors, RNA Splicing, RNA, Messenger, Spliceosomes, Two-Hybrid System Techniques
Biochem. J.
Date: Feb. 15, 2004
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