title: Sip1, a novel RS domain-containing protein essential for pre-mRNA splicing.
abstract: Previous studies have shown that protein-protein interactions among splicing factors may play an important role in pre-mRNA splicing. We report here identification and functional characterization of a new splicing factor, Sip1 (SC35-interacting protein 1). Sip1 was initially identified by virtue of its interaction with SC35, a splicing factor of the SR family. Sip1 interacts with not only several SR proteins but also with U1-70K and U2AF65, proteins associated with 5' and 3' splice sites, respectively. The predicted Sip1 sequence contains an arginine-serine-rich (RS) domain but does not have any known RNA-binding motifs, indicating that it is not a member of the SR family. Sip1 also contains a region with weak sequence similarity to the Drosophila splicing regulator suppressor of white apricot (SWAP). An essential role for Sip1 in pre-mRNA splicing was suggested by the observation that anti-Sip1 antibodies depleted splicing activity from HeLa nuclear extract. Purified recombinant Sip1 protein, but not other RS domain-containing proteins such as SC35, ASF/SF2, and U2AF65, restored the splicing activity of the Sip1-immunodepleted extract. Addition of U2AF65 protein further enhanced the splicing reconstitution by the Sip1 protein. Deficiency in the formation of both A and B splicing complexes in the Sip1-depleted nuclear extract indicates an important role of Sip1 in spliceosome assembly. Together, these results demonstrate that Sip1 is a novel RS domain-containing protein required for pre-mRNA splicing and that the functional role of Sip1 in splicing is distinct from those of known RS domain-containing splicing factors.
authors.affiliation: Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: W J
authors.initials: WJ
authors.lastname: Zhang
authors.forename: J Y
authors.initials: JY
authors.lastname: Wu
mesh_terms: D000595:Amino Acid Sequence; D005656:Fungal Proteins / Q000276:immunology / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007106:Immune Sera; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D012322:RNA Precursors / Q000378:metabolism*; D012326:RNA Splicing; D011994:Recombinant Proteins / Q000378:metabolism; D017412:Ribonucleoprotein, U1 Small Nuclear / Q000378:metabolism; D012261:Ribonucleoproteins; D000068103:Serine-Arginine Splicing Factors; D017381:Spliceosomes / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D007106:Immune Sera; D009687:Nuclear Proteins; D012322:RNA Precursors; D011994:Recombinant Proteins; D017412:Ribonucleoprotein, U1 Small Nuclear; D012261:Ribonucleoproteins; C490688:SNRNP70 protein, human; C073288:SRSF2 protein, human; D000068103:Serine-Arginine Splicing Factors