title: SIPP1, a novel pre-mRNA splicing factor and interactor of protein phosphatase-1.
abstract: 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.
authors.affiliation: Departamento de Biologia Molecular, Facultad de Medicina, Universidad de Cantabria, Unidad Asociada al CIB-CSIC, 39011 Santander, Spain.
authors.forename: Miriam
authors.initials: M
authors.lastname: Llorian
authors.forename: Monique
authors.initials: M
authors.lastname: Beullens
authors.forename: Isabel
authors.initials: I
authors.lastname: Andrés
authors.forename: Jose-Miguel
authors.initials: JM
authors.lastname: Ortiz
authors.forename: Mathieu
authors.initials: M
authors.lastname: Bollen
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D010749:Phosphoprotein Phosphatases / Q000737:chemistry / Q000378:metabolism*; D054645:Protein Phosphatase 1; D011506:Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D012322:RNA Precursors / Q000378:metabolism*; D012326:RNA Splicing; D000072260:RNA Splicing Factors; D012333:RNA, Messenger / Q000378:metabolism*; D017381:Spliceosomes / Q000737:chemistry; D020798:Two-Hybrid System Techniques
chemical_list: D004268:DNA-Binding Proteins; D011506:Proteins; D012322:RNA Precursors; D000072260:RNA Splicing Factors; D012333:RNA, Messenger; C483880:Wbp11 protein, mouse; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1