title: A human importin-beta family protein, transportin-SR2, interacts with the phosphorylated RS domain of SR proteins.
abstract: Serine/arginine-rich proteins (SR proteins) are mainly involved in the splicing of precursor mRNA. RS domains are also found in proteins that have influence on other aspects of gene expression. Proteins that contain an RS domain are often located in the speckled domains of the nucleus. Here we show that the RS domain derived from a human papillomavirus E2 transcriptional activator can target a heterologous protein to the nucleus, as it does in many other SR proteins, but insufficient for localization in speckles. By using E2 as a bait in a yeast two-hybrid screen, we identified a human importin-beta family protein that is homologous to yeast Mtr10p and almost identical to human transportin-SR. This transportin-SR2 (TRN-SR2) protein can interact with several cellular SR proteins. More importantly, we demonstrated that TRN-SR2 can directly interact with phosphorylated, but not unphosphorylated, RS domains. Finally, an indirect immunofluoresence study revealed that a transiently expressed TRN-SR2 mutant lacking the N-terminal region becomes localized to the nucleus in a speckled pattern that coincides with the distribution of the SR protein SC35. Thus, our results likely reflect a role of TRN-SR2 in the cellular trafficking of phosphorylated SR proteins.
authors.affiliation: Institute of Biomedical Sciences, Academia Sinica, Nankang, Taipei 11529, Taiwan.
authors.forename: M C
authors.initials: MC
authors.lastname: Lai
authors.forename: R I
authors.initials: RI
authors.lastname: Lin
authors.forename: S Y
authors.initials: SY
authors.lastname: Huang
authors.forename: C W
authors.initials: CW
authors.lastname: Tsai
authors.forename: W Y
authors.initials: WY
authors.lastname: Tarn
mesh_terms: D020816:Amino Acid Motifs; D001120:Arginine; D001665:Binding Sites; D001692:Biological Transport; D002451:Cell Compartmentation; D002467:Cell Nucleus / Q000648:ultrastructure; D019084:Fluorescent Antibody Technique, Indirect; D006367:HeLa Cells; D006801:Humans; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000302:isolation & purification; D027383:Papillomaviridae; D010750:Phosphoproteins / Q000378:metabolism*; D011485:Protein Binding; D018160:Receptors, Cytoplasmic and Nuclear / Q000302:isolation & purification*; D012261:Ribonucleoproteins; D012694:Serine; D000068103:Serine-Arginine Splicing Factors; D020798:Two-Hybrid System Techniques; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism; D028961:beta Karyopherins
chemical_list: D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D010750:Phosphoproteins; D018160:Receptors, Cytoplasmic and Nuclear; D012261:Ribonucleoproteins; D014764:Viral Proteins; D028961:beta Karyopherins; C119888:transportin SR; C073288:SRSF2 protein, human; D000068103:Serine-Arginine Splicing Factors; D012694:Serine; D001120:Arginine