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© The Rockefeller University Press,
0021-9525/1999//1145 $5.00
The Journal of Cell Biology, Volume 145, Number 6,
, 1999 1145-1152
Article |
Transportin-SR, a Nuclear Import Receptor for SR Proteins
The SR proteins, a group of abundant arginine/serine (RS)-rich proteins, are essential pre-mRNA splicing factors that are localized in the nucleus. The RS domain of these proteins serves as a nuclear localization signal. We found that RS domain–bearing proteins do not utilize any of the known nuclear import receptors and identified a novel nuclear import receptor specific for SR proteins. The SR protein import receptor, termed transportin-SR (TRN-SR), binds specifically and directly to the RS domains of ASF/SF2 and SC35 as well as several other SR proteins. The nuclear transport regulator RanGTP abolishes this interaction. Recombinant TRN-SR mediates nuclear import of RS domain– bearing proteins in vitro. TRN-SR has amino acid sequence similarity to several members of the importin β/transportin family. These findings strongly suggest that TRN-SR is a nuclear import receptor for the SR protein family.
Key Words: SR proteins • RS domain • nuclear localization signal • nuclear import receptor • RanGTP
Abbreviations used in this paper: GST, glutathione-S-transferase; hnRNP, heterogeneous nuclear RNP; IBB, importin β–binding domain; MBP, maltose-binding protein; NLS, nuclear localization signal; NPC, nuclear pore complex; RS domain, arginine/serine rich domain; TRN1, transportin 1; TRN-SR, transportin-SR.
Address correspondence to Gideon Dreyfuss, Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, 415 Curie Blvd., Clinical Research Building, Room 328, Philadelphia, PA 19104-6148. Tel.: 215-898-0398. Fax: 215-573-2000. E-mail: gdreyfuss{at}hhmi.upenn.edu
IN eukaryotic cells, trafficking of proteins and RNAs between the cytoplasm and the nucleus occurs through large structures in the nuclear envelope, called nuclear pore complexes (NPCs)1 (for reviews see Doye and Hurt, 1997; Nakielny and Dreyfuss, 1997; Izaurralde and Adam, 1998; Ohno et al., 1998; Pemberton et al., 1998; Stutz and Rosbash, 1998). Although small molecules of <60 kD can generally diffuse into the nucleus, most nuclear proteins have nuclear localization signals (NLSs) that mediate their active import into the nucleus. The most extensively characterized NLS is the classical NLS which consists of a short segment of basic amino acids (Kalderon et al., 1984; Robbins et al., 1991). The nuclear import of proteins containing this NLS is mediated by a dimeric soluble factor comprised of importins 
and β (also referred to as karyopherins and β; Görlich et al., 1994, 1995; Chi et al., 1995; Imamoto et al., 1995a,b; Moroianu et al., 1995; Radu et al., 1995). Importin binds the NLS directly and serves as the adapter to importin β, which interacts with the NLS-importin complex through the importin β–binding domain (IBB) of importin (Görlich et al., 1996a; Moroianu et al., 1996a; Weis et al., 1996). The other well characterized NLS is the M9 sequence of heterogeneous nuclear RNP (hnRNP) A1 (Siomi and Dreyfuss, 1995; Weighardt et al., 1995). M9-dependent import is mediated by transportin 1 (TRN1, also referred to as karyopherin β2 or MIP) which is related by sequence to importin β. Unlike importin β, which utilizes importin as an adapter for NLS binding, TRN1 binds to M9 directly (Nakielny et al., 1996; Pollard et al., 1996; Bonifaci et al., 1997; Fridell et al., 1997). By sequence homology searches or biochemical purification, several importin β/TRN1–related proteins have been identified in several species (Görlich et al., 1997). Some of these have been found to be nuclear import or nuclear export receptors for specific proteins and RNAs (reviewed in Weis, 1998; Wozniak et al., 1998). Importin β homologues are all similar in size (95–125 kD) and show considerable amino acid sequence similarity, particularly in their amino-terminal regions which have been shown to contain a RanGTP-binding domain (Görlich et al., 1997). Ran is a small GTPase that can exist in either a GTP-bound state (RanGTP) or a GDP-bound state (RanGDP) (reviewed by Dahlberg and Lund, 1998; Moore, 1998). One role of RanGTP, considered to be the predominant form of Ran in the nucleus, is to promote dissociation of import receptor-cargo complexes and thus cause cargo release in the nucleus (Rexach and Blobel, 1995; Chi et al., 1996; Görlich et al., 1996b; Moroianu et al., 1996b; Izaurralde et al., 1997; Siomi et al., 1997). RanGTP also plays an important role in nuclear export as it is required for efficient binding of export receptors to their cargoes (Fornerod et al., 1997; Kutay et al., 1997b, 1998; Arts et al., 1998).
In addition to the two NLSs described above, the arginine/serine rich (RS) domain of SR proteins has been shown also to function as an NLS (Li and Bingham, 1991; Hedley et al., 1995; Cáceres et al., 1997). SR proteins are essential splicing factors, characterized by the presence of at least one RNA-binding domain and a domain containing several, often numerous, arginine/serine dipeptide repeats (for review see Fu, 1995). Several SR proteins have been described including SRp20, 30 (ASF/SF2, SC35), 40, 55, and 75 (Fu and Maniatis, 1990, 1992; Ge and Manley, 1990; Krainer et al., 1990, 1991; Ge et al., 1991; Zahler et al., 1992, 1993). In addition to their roles as essential splicing factors, SR proteins can modulate splice site selection and thus also have important regulatory roles in alternative splicing (Ge and Manley, 1990; Krainer et al., 1990, 1991; Ge et al., 1991; Fu et al., 1992; Zahler et al., 1993; Cáceres et al., 1994). SR proteins are generally found throughout the nucleoplasm and are often particularly concentrated in nuclear speckles, or interchromatin granules (Fu and Maniatis, 1990; Fu, 1995; Cáceres et al., 1997; Singer and Green, 1997; Lamond and Earnshaw, 1998; Misteli and Spector, 1998). Several of the SR proteins have also been shown to shuttle between the nucleus and the cytoplasm (Cáceres et al., 1998) and to accompany mRNAs as they are exported through the NPC (Alzhanova-Ericsson et al., 1996).
Although the RS domain has been shown to function as an NLS for SR proteins and to participate in their localization to speckles (Li and Bingham, 1991; Hedley et al., 1995; Cáceres et al., 1997), the nuclear import pathway for SR proteins has not been previously characterized. Here we show that the nuclear import of several of the SR proteins, including ASF/SF2 and SC35, is mediated by a specific import receptor, termed transportin-SR (TRN-SR). TRN-SR is a novel member of the importin β/transportin family and we show that it binds specifically and directly to the RS domains of ASF/SF2, SC35, and to several additional SR proteins. These findings indicate that TRN-SR is the nuclear import receptor for many SR proteins.
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In Vitro Nuclear Import Assays
Nuclear import assays were performed as described (Pollard et al., 1996). Rabbit reticulocyte lysate (Promega) was used as a cytosol source and prepared as described previously (Adam et al., 1990). The transport substrates were added at a concentration of 50 µg/ml. For competition experiments with maltose-binding protein (MBP) fusion proteins, competitors (1 mg/ml) were added to the complete transport mix except transport substrate, incubated on ice for 15 min, and then combined with transport substrate and nuclei. For the import experiments with recombinant receptor protein, recombinant His-tagged TRN-SR and His-tagged RanGDP were added at concentrations of 120 and 40 µg/ml, respectively.
Yeast Two-Hybrid Interaction Screening
The HeLa MATCHMAKER LexA cDNA library, yeast strains, and cloning vectors were obtained from Clontech, Inc. All library screening and yeast manipulations were carried out as recommended by the manufacturer. Saccharomyces cerevisiae strain EGY48 was transformed simultaneously with pLexA-ASF/SF2 RS and the HeLa cell cDNA library. 2 x 106 transformants were plated onto 20 150-mm plates of X-gal–synthetic medium lacking histidine, uracil, tryptophan, and leucine. 32 Leu+ growers that had shown blue color on those plates were isolated. Insert cDNAs were amplified by PCR on these yeast cells using the Advantage-HFTM PCR kit (Clontech, Inc.) and sequenced.
Full-Length TRN-SR Isolation
The PCR fragment from clone 1-1 was used as a hybridization probe to screen the 
phage HeLa cell cDNA library (Clontech, Inc.). Several clones were isolated, and the clone that had the longest insert was sequenced and thus determined as the full-length coding sequence of TRN-SR.
Protein-binding Assays
TRN-SR was produced by in vitro transcription-translation of His-TRN-SR, using a TNT kit (Promega) in rabbit reticulocyte lysate in the presence of [35S]methionine (Amersham) according to the procedure that the manufacturer recommends. Purified recombinant GST and GST fusion proteins (5 µg each) were immobilized on 50 µl of glutathione-Sepharose (Pharmacia) in PBS for at least 1 h at 4°C. The resin was washed with 500 µl of binding buffer (50 mM Tris-HCl, 400 mM NaCl, 5 mM MgOAc, 2 µg/ml of leupeptin, 2 µg/ml of pepstatin, 1% aprotinin, and 0.05% [wt/vol] digitonin; Calbiochem). In vitro translated TRN-SR was added and incubated with these immobilized proteins for 1 h at 4°C. For the experiments to check the effect of exogenous Ran protein, His-tagged RanQ69L (GTP form) was added at a concentration of 2 µM. The resin was washed with 500 µl of binding buffer five times and the bound fraction was eluted by boiling in SDS-PAGE sample buffer. The bound fraction was then analyzed by SDS-PAGE and visualized by fluorography.
The binding experiments with recombinant proteins were done essentially as described above except 20 µg of His- and T7-tagged recombinant TRN-SR was used. Binders were analyzed by 12.5% SDS-PAGE, and detected by an anti-T7 monoclonal antibody (Novagen) and ECL system (Amersham).
Far Western Blotting with SR Proteins
Purified SR proteins were kindly provided by Dr. Akila Mayeda prepared from HeLa cells as described previously (Zahler et al., 1992). 10 µg of proteins was analyzed by SDS-PAGE and transferred to nitrocellulose membrane. Far Western blotting was performed as described previously (Siomi et al., 1997) by using either TRN-SR or TRN1 produced by a TNT kit (Promega) in rabbit reticulocyte lysate in the presence of [35S]methionine (Amersham).
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N44), reagents which block active nuclear import through NPCs (Forbes, 1992; Görlich et al., 1996b; Kutay et al., 1997a), completely abolished GST-ASF/SF2 RS nuclear import (Fig. 1).
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The 1-1 DNA insert was subcloned and used for hybridization screening of a phage HeLa cDNA library. A 3-kb clone that appears to contain the entire coding region was obtained. The predicted amino acid sequence of this protein, which we termed TRN-SR, because it turned out, like TRN1, to be a transport receptor of pre-mRNA/mRNA-binding proteins, is shown in Fig. 3. TRN-SR is a 975– amino acid protein with a calculated molecular mass of 109,838 D and an estimated pI of 5.29. The amino-terminal domain of TRN-SR shows significant sequence similarity to other importin β/transportin family members, including a region required for RanGTP binding (Görlich et al., 1997). The sequence of the original 1-1 clone isolated from the yeast two-hybrid screening starts at amino acid 590 of the TRN-SR sequence and contains the entire COOH-terminal domain. A BLAST homology search with full-length TRN-SR revealed three proteins that bear significant homology to TRN-SR in other species (Fig. 3). The most similar of these, AF025464 of Caenorhabditis elegans, is 26% identical and 45% similar to TRN-SR. Another apparent homologue is AL022304 of Schizosaccharomyces pombe that is 25% identical and 46% similar, although this clone does not appear to contain the full-length protein sequence. These two sequences are the two closest orthologues of TRN-SR present in available databases. Of previously characterized proteins, the most significant similarity is found with the S. cerevisiae protein Mtr10p (Kadowaki et al., 1994) which has been shown recently to be a nuclear import receptor for Npl3p (Pemberton et al., 1997; Senger et al., 1998). Npl3p is an hnRNP protein in yeast (Bossie et al., 1992; Russell and Tollervey, 1992; Wilson et al., 1994). The amino acid sequences of TRN-SR and Mtr10p are 21% identical and 42% similar.
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33 kD, that likely correspond to ASF/SF2 and SC35, proteins of 20, 46, and 55 kD also bound specifically to TRN-SR. This observed profile is similar to that detected by Western blotting with mAb104 (Fig. 6), suggesting that TRN-SR is a common nuclear import receptor for many of the SR proteins.
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TRN-SR binds to the RS domain of ASF/SF2 and of SC35, and these interactions are disrupted by RanQ69L (Fig. 4 A). Furthermore, TRN-SR also binds other proteins enriched in an SR protein fraction (Fig. 6). These results strongly suggest that TRN-SR is a general nuclear import receptor for SR proteins. However, we note that no binding of TRN-SR to SRp75 was detected by far Western blotting, although this protein is abundant in the fraction we tested (Fig. 6). The reason for this is unknown, but it is possible that SRp75 may have a different receptor. There are additional SR proteins, including pre-mRNA splicing factors such as 9G8, U170K, U2AF35, and 65 (Fu, 1995), as well as two large SR proteins (Blencowe et al., 1998), and it remains to be determined whether TRN-SR also mediates the nuclear import of these proteins.
Several abundant hnRNP proteins, including hnRNP A1, A2, and F, are imported by TRN1 (Pollard et al., 1996; Siomi et al., 1997). Thus, in mammalian cells there are at least two nuclear import pathways for pre-mRNA/ mRNA-binding proteins, one mediated by TRN1 and one by TRN-SR. The relative amounts of hnRNP proteins and SR proteins are important for alternative pre-mRNA splicing. For example, the ratio between hnRNP A1 and ASF/SF2 affects 5' splice site selection (Mayeda and Krainer, 1992; Zahler et al., 1993; Cáceres et al., 1994; Yang et al., 1994). As both of these proteins shuttle between the nucleus and the cytoplasm (Piñol-Roma and Dreyfuss, 1992; Alzhanova-Ericsson et al., 1996; Cáceres et al., 1998), it is conceivable that their relative amounts in the nucleus may be controlled by regulating their rates of nuclear import. Thus, by modifying either the transportins themselves or the respective NLSs, M9 and RS, splice site selection could be modulated. Indeed, several protein kinases have been reported to phosphorylate serine residues in the RS domains of SR proteins (Gui et al., 1994a,b; Colwill et al., 1996; Rossi et al., 1996; Kuroyanagi et al., 1998; Okamoto et al., 1998; Wang et al., 1998). While overexpression of some of these SR protein kinases causes disruption of nuclear speckles (Gui et al., 1994a; Kuroyanagi et al., 1998; Wang et al., 1998), they do not disrupt the nuclear localization of SR proteins. However, overexpression of one SR protein kinase, Clk/Sty kinase, does cause cytoplasmic accumulation of ASF/SF2 in HeLa cells (Cáceres et al., 1998). More recently it was reported that overexpression of kinase-inactive mutant of SR protein kinase-2 causes cytoplasmic accumulation of ASF/SF2 (Koizumi et al., 1999). It will be interesting to determine the effect of RS domain phosphorylation on the SR proteins–TRN-SR interaction.
The physiological function of the shuttling of SR proteins is not known. Both hnRNP A1/A2 proteins and SR proteins are associated with the same mRNAs as they are exported to the cytoplasm (Alzhanova-Ericsson, 1996; Visa et al., 1996) and it is thus possible that they both play a role in mRNA export. Nuclear export signals in the shuttling SR proteins have not been identified yet. The identification of nuclear export signals in shuttling SR proteins, if such exist, and of export receptors for them are issues of considerable interest that remain to be clarified.
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Acknowledgments |
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N44 protein and RanQ69L expression plasmids; and Dr. Akila Mayeda for SR proteins. We also thank Lili Wan for help on yeast two-hybrid library screening, and other members of our laboratory, especially Drs. Sara Nakielny, Haruhiko Siomi, Lili Wan, and Robert Perkinson for critical reading and comments on the manuscript. This work was supported by a grant from the National Institutes of Health (G. Dreyfuss), and by a long-term fellowship from Human Frontier Science Program Organization (N. Kataoka). G. Dreyfuss is an Investigator of the Howard Hughes Medical Institute.
Submitted: 16 February 1999
Revised: 5 May 1999
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References |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Adam SA, Marr RS & Gerace L. Nuclear protein import in permeabilized mammalian cells requires soluble cytoplasmic factors, J Cell Biol, 1990, 111, 807–816.
Alzhanova-Ericsson AT, Sun X, Visa N, Kiseleva E, Wurtz T & Daneholt B. A protein of the SR family of splicing factors binds extensively to exonic Balbiani ring pre-mRNA and accompanies the RNA from the gene to the nuclear pore, Genes Dev, 1996, 10, 2881–2893.
Arts GJ, Fornerod M & Mattaj IW. Identification of a nuclear export receptor for tRNA, Curr Biol, 1998, 8, 305–314.[Medline]
Blencowe BJ, Issner R, Nickerson JA & Sharp PA. A coactivator of pre-mRNA splicing, Genes Dev, 1998, 12, 996–1009.
Bonifaci N, Moroianu J, Radu A & Blobel G. Karyopherin beta2 mediates nuclear import of a mRNA binding protein, Proc Natl Acad Sci USA, 1997, 94, 5055–5060.
Bossie MA, DeHoratius C, Barcelo G & Silver P. A mutant nuclear protein with similarity to RNA binding proteins interferes with nuclear import in yeast, Mol Biol Cell, 1992, 3, 875–893.[Abstract]
Cáceres JF, Stamm S, Helfman DM & Krainer AR. Regulation of alternative splicing in vivo by overexpression of antagonistic splicing factors, Science, 1994, 265, 1706–1709.
Cáceres JF, Misteli T, Screaton GR, Spector DL & Krainer AR. Role of the modular domains of SR proteins in subnuclear localization and alternative splicing specificity, J Cell Biol, 1997, 138, 225–238.
Cáceres JF, Screaton GR & Krainer AR. A specific subset of SR proteins shuttles continuously between the nucleus and the cytoplasm, Genes Dev, 1998, 12, 55–66.
Chi NC, Adam EJ & Adam SA. Sequence and characterization of cytoplasmic nuclear protein import factor p97, J Cell Biol, 1995, 130, 265–274.
Chi NC, Adam EJ, Visser GD & Adam SA. RanBP1 stabilizes the interaction of Ran with p97 nuclear protein import, J Cell Biol, 1996, 135, 559–569.
Colwill K, Pawson T, Andrews B, Prasad J, Manley JL, Bell JC & Duncan PI. The Clk/Sty protein kinase phosphorylates SR splicing factors and regulates their intranuclear distribution, EMBO (Eur Mol Biol Organ) J, 1996, 15, 265–275.[Medline]
Dahlberg JE & Lund E. Functions of the GTPase Ran in RNA export from the nucleus, Curr Opin Cell Biol, 1998, 10, 400–408.[Medline]
Doye V & Hurt E. From nucleoporins to nuclear pore complexes, Curr Opin Cell Biol, 1997, 9, 401–411.[Medline]
Forbes DJ. Structure and function of the nuclear pore complex, Annu Rev Cell Biol, 1992, 8, 495–527.
Fornerod M, Ohno M, Yoshida M & Mattaj IW. CRM1 is an export receptor for leucine-rich nuclear export signals, Cell, 1997, 90, 1051–1060.[Medline]
Fridell RA, Truant R, Thorne L, Benson RE & Cullen BR. Nuclear import of hnRNP A1 is mediated by a novel cellular cofactor related to karyopherin-beta, J Cell Sci, 1997, 110, 1325–1331.[Abstract]
Fu X-D. The superfamily of arginine/serine-rich splicing factors, RNA, 1995, 1, 663–680.[Medline]
Fu X-D & Maniatis T. Factor required for mammalian spliceosome assembly is localized to discrete regions in the nucleus, Nature, 1990, 343, 437–441.[Medline]
Fu X-D & Maniatis T. Isolation of a complementary DNA that encodes the mammalian splicing factor SC35, Science, 1992, 256, 535–538.
Fu X-D, Mayeda A, Maniatis T & Krainer AR. General splicing factors SF2 and SC35 have equivalent activities in vitro, and both affect alternative 5' and 3' splice site selection, Proc Natl Acad Sci USA, 1992, 89, 11224–11228.
Ge H & Manley JL. A protein factor, ASF, controls cell-specific alternative splicing of SV40 early pre-mRNA in vitro, Cell, 1990, 62, 25–34.[Medline]
Ge H, Zuo P & Manley JL. Primary structure of the human splicing factor ASF reveals similarities with Drosophilaregulators, Cell, 1991, 66, 373–382.[Medline]
Görlich D, Prehn S, Laskey RA & Hartmann E. Isolation of a protein that is essential for the first step of nuclear protein import, Cell, 1994, 79, 767–778.[Medline]
Görlich D, Kostka S, Kraft R, Dingwall C, Laskey RA, Hartmann E & Prehn S. Two different subunits of importin cooperate to recognize nuclear localization signals and bind them to the nuclear envelope, Curr Biol, 1995, 5, 383–392.[Medline]
Görlich D, Henklein P, Laskey RA & Hartmann E. A 41 amino acid motif in importin-alpha confers binding to importin-beta and hence transit into the nucleus, EMBO (Eur Mol Biol Organ) J, 1996a, 15, 1810–1817.[Medline]
Görlich D, Pante N, Kutay U, Aebi U & Bischoff FR. Identification of different roles for RanGDP and RanGTP in nuclear protein import, EMBO (Eur Mol Biol Organ) J, 1996b, 15, 5584–5594.[Medline]
Görlich D, Dabrowski M, Bischoff FR, Kutay U, Bork P, Hartmann E, Prehn S & Izaurralde E. A novel class of RanGTP binding proteins, J Cell Biol, 1997, 138, 65–80.
Gross T, Richert K, Mierke C, Lutzelberger M & Kaufer NF. Identification and characterization of srp1, a gene of fission yeast encoding a RNA binding domain and a RS domain typical of SR splicing factors, Nucl Acids Res, 1998, 26, 505–511.
Gui JF, Lane WS & Fu X-D. A serine kinase regulates intracellular localization of splicing factors in the cell cycle, Nature, 1994a, 369, 678–682.[Medline]
Gui JF, Tronchere H, Chandler SD & Fu X-D. Purification and characterization of a kinase specific for the serine- and arginine-rich pre-mRNA splicing factors, Proc Natl Acad Sci USA, 1994b, 91, 10824–10828.
Hedley ML, Amrein H & Maniatis T. An amino acid sequence motif sufficient for subnuclear localization of an arginine/serine-rich splicing factor, Proc Natl Acad Sci USA, 1995, 92, 11524–11528.
Imamoto N, Shimamoto T, Kose S, Takao T, Tachibana T, Matsubae M, Sekimoto T, Shimonishi Y & Yoneda Y. The nuclear pore-targeting complex binds to nuclear pores after association with a karyophile, FEBS Lett, 1995a, 368, 415–419.[Medline]
Imamoto N, Shimamoto T, Takao T, Tachibana T, Kose S, Matsubae M, Sekimoto T, Shimonishi Y & Yoneda Y. In vivo evidence for involvement of a 58 kD component of nuclear pore-targeting complex in nuclear protein import, EMBO (Eur Mol Biol Organ) J, 1995b, 14, 3617–3626.[Medline]
Izaurralde E & Adam S. Transport of macromolecules between the nucleus and the cytoplasm, RNA, 1998, 4, 351–364.[Abstract]
Izaurralde E, Kutay U, von Kobbe C, Mattaj IW & Görlich D. The asymmetric distribution of the constituents of the Ran system is essential for transport into and out of the nucleus, EMBO (Eur Mol Biol Organ) J, 1997, 16, 6535–6547.[Medline]
Kadowaki T, Chen S, Hitomi M, Jacobs E, Kumagai C, Liang S, Schneiter R, Singleton D, Wisniewska J & Tartakoff AM. Isolation and characterization of Saccharomyces cerevisiaemRNA transport-defective (mtr) mutants, J Cell Biol, 1994, 126, 649–659.
Kalderon D, Roberts BL, Richardson WD & Smith AE. A short amino acid sequence able to specify nuclear location, Cell, 1984, 39, 499–509.[Medline]
Klebe C, Bischoff FR, Ponstingl H & Wittinghofer A. Interaction of the nuclear GTP-binding protein Ran with its regulatory proteins RCC1 and RanGAP1, Biochemistry, 1995, 34, 639–647.[Medline]
Koizumi J, Okamoto Y, Onogi H, Mayeda A, Krainer AR & Hagiwara M. The subcellular localization of SF2/ASF is regulated by direct interaction with SR protein kinases (SRPKs), J Biol Chem, 1999, 274, 11125–11131.
Krainer AR, Conway GC & Kozak D. The essential pre-mRNA splicing factor SF2 influences 5' splice site selection by activating proximal sites, Cell, 1990, 62, 35–42.[Medline]
Krainer AR, Mayeda A, Kozak D & Binns G. Functional expression of cloned human splicing factor SF2: homology to RNA-binding proteins, U170K, and Drosophilasplicing regulators, Cell, 1991, 66, 383–394.[Medline]
Kuroyanagi N, Onogi H, Wakabayashi T & Hagiwara M. Novel SR-protein-specific kinase, SRPK2, disassembles nuclear speckles, Biochem Biophys Res Commun, 1998, 242, 357–364.[Medline]
Kutay U, Izaurralde E, Bischoff FR, Mattaj IW & Görlich D. Dominant-negative mutants of importin-beta block multiple pathways of import and export through the nuclear pore complex, EMBO (Eur Mol Biol Organ) J, 1997a, 16, 1153–1163.[Medline]
Kutay U, Bischoff FR, Kostka S, Kraft R & Görlich D. Export of importin alpha from the nucleus is mediated by a specific nuclear transport factor, Cell, 1997b, 90, 1061–1071.[Medline]
Kutay U, Lipowsky G, Izaurralde E, Bischoff FR, Schwarzmaier P, Hartmann E & Görlich D. Identification of a tRNA-specific nuclear export receptor, Mol Cell, 1998, 1, 359–369.[Medline]
Lamond AI & Earnshaw WC. Structure and function in the nucleus, Science, 1998, 280, 547–553.
Li H & Bingham PM. Arginine/serine-rich domains of the su(wa) and tra RNA processing regulators target proteins to a subnuclear compartment implicated in splicing, Cell, 1991, 67, 335–342.[Medline]
Mayeda A & Krainer AR. Regulation of alternative pre-mRNA splicing by hnRNP A1 and splicing factor SF2, Cell, 1992, 68, 365–375.[Medline]
Misteli T & Spector DL. The cellular organization of gene expression, Curr Opin Cell Biol, 1998, 10, 323–331.[Medline]
Moore MS. Ran and nuclear transport, J Biol Chem, 1998, 273, 22857–22860.
Moroianu J, Blobel G & Radu A. Previously identified protein of uncertain function is karyopherin alpha and together with karyopherin beta docks import substrate at nuclear pore complexes, Proc Natl Acad Sci USA, 1995, 92, 2008–2011.
Moroianu J, Blobel G & Radu A. The binding site of karyopherin alpha for karyopherin beta overlaps with a nuclear localization sequence, Proc Natl Acad Sci USA, 1996a, 93, 6572–6576.
Moroianu J, Blobel G & Radu A. Nuclear protein import: Ran-GTP dissociates the karyopherin alphabeta heterodimer by displacing alpha from an overlapping binding site on beta, Proc Natl Acad Sci USA, 1996b, 93, 7059–7062.
Nakielny S & Dreyfuss G. Nuclear export of proteins and RNAs, Curr Opin Cell Biol, 1997, 9, 420–429.[Medline]
Nakielny S, Siomi MC, Siomi H, Michael WM, Pollard V & Dreyfuss G. Transportin: nuclear transport receptor of a novel nuclear protein import pathway, Exp Cell Res, 1996, 229, 261–266.[Medline]
Ohno M, Fornerod M & Mattaj IW. Nucleocytoplasmic transport: the last 200 nanometers, Cell, 1998, 92, 327–336.[Medline]
Okamoto Y, Onogi H, Honda R, Yasuda H, Wakabayashi T, Nimura Y & Hagiwara M. cdc2 kinase-mediated phosphorylation of splicing factor SF2/ASF, Biochem Biophys Res Commun, 1998, 249, 872–878.[Medline]
Pemberton LF, Rosenblum JS & Blobel G. A distinct and parallel pathway for the nuclear import of an mRNA-binding protein, J Cell Biol, 1997, 139, 1645–1653.
Pemberton LF, Blobel G & Rosenblum JS. Transport routes through the nuclear pore complex, Curr Opin Cell Biol, 1998, 10, 392–399.[Medline]
Piñol-Roma S & Dreyfuss G. Shuttling of pre-mRNA binding proteins between nucleus and cytoplasm, Nature, 1992, 355, 730–732.[Medline]
Pollard VW, Michael WM, Nakielny S, Siomi MC, Wang F & Dreyfuss G. A novel receptor-mediated nuclear protein import pathway, Cell, 1996, 86, 985–994.[Medline]
Radu A, Blobel G & Moore MS. Identification of a protein complex that is required for nuclear protein import and mediates docking of import substrate to distinct nucleoporins, Proc Natl Acad Sci USA, 1995, 92, 1769–1773.
Rexach M & Blobel G. Protein import into nuclei: association and dissociation reactions involving transport substrate, transport factors, and nucleoporins, Cell, 1995, 83, 683–692.[Medline]
Robbins J, Dilworth SM, Laskey RA & Dingwall C. Two interdependent basic domains in nucleoplasmin nuclear targeting sequence: identification of a class of bipartite nuclear targeting sequence, Cell, 1991, 64, 615–623.[Medline]
Rossi F, Labourier E, Forne T, Divita G, Derancourt J, Riou JF, Antoine E, Cathala G, Brunel C & Tazi J. Specific phosphorylation of SR proteins by mammalian DNA topoisomerase I, Nature, 1996, 381, 80–82.[Medline]
Russell ID & Tollervey D. NOP3 is an essential yeast protein which is required for pre-rRNA processing, J Cell Biol, 1992, 119, 737–747.
Senger B, Simos G, Bischoff FR, Podtelejnikov A, Mann M & Hurt E. Mtr10p functions as a nuclear import receptor for the mRNA-binding protein Npl3p, EMBO (Eur Mol Biol Organ) J, 1998, 17, 2196–2207.[Medline]
Siebel CW & Guthrie C. The essential yeast RNA binding protein Np13p is methylated, Proc Natl Acad Sci USA, 1996, 93, 13641–13646.
Singer RH & Green MR. Compartmentalization of eukaryotic gene expression: causes and effects, Cell, 1997, 91, 291–294.[Medline]
Siomi H & Dreyfuss G. A nuclear localization domain in the hnRNP A1 protein, J Cell Biol, 1995, 129, 551–560.
Siomi MC, Eder PS, Kataoka N, Wan L, Liu Q & Dreyfuss G. Transportin-mediated nuclear import of heterogeneous nuclear RNP proteins, J Cell Biol, 1997, 138, 1181–1192.
Stutz F & Rosbash M. Nuclear RNA export, Genes Dev, 1998, 12, 3303–3319.
Visa N, Alzhanova-Ericsson AT, Sun X, Kiseleva E, Bjorkroth B, Wurtz T & Daneholt B. A pre-mRNA-binding protein accompanies the RNA from the gene through the nuclear pores and into polysomes, Cell, 1996, 84, 253–264.[Medline]
Wang HY, Lin W, Dyck JA, Yeakley JM, Songyang Z, Cantley LC & Fu X-D. SRPK2: a differentially expressed SR protein-specific kinase involved in mediating the interaction and localization of pre-mRNA splicing factors in mammalian cells, J Cell Biol, 1998, 140, 737–750.
Weighardt F, Biamonti G & Riva S. Nucleo-cytoplasmic distribution of human hnRNP proteins: a search for the targeting domains in hnRNP A1, J Cell Sci, 1995, 108, 545–555.[Abstract]
Weis K. Importins and exportins: how to get in and out of the nucleus, Trends Biochem Sci, 1998, 23, 185–189.[Medline]
Weis K, Ryder U & Lamond AI. The conserved amino-terminal domain of hSRP1 alpha is essential for nuclear protein import, EMBO (Eur Mol Biol Organ) J, 1996, 15, 1818–1825.[Medline]
Wilson SM, Datar KV, Paddy MR, Swedlow JR & Swanson MS. Characterization of nuclear polyadenylated RNA-binding proteins in Saccharomyces cerevisiae. , J Cell Biol, 1994, 127, 1173–1184.
Wozniak RW, Rout MP & Aitchison JD. Karyopherins and kissing cousins, Trends Cell Biol, 1998, 8, 184–188.[Medline]
Yang X, Bani MR, Lu SJ, Rowan S, Ben-David Y & Chabot B. The A1 and A1B proteins of heterogeneous nuclear ribonucleoparticles modulate 5' splice site selection in vivo, Proc Natl Acad Sci USA, 1994, 91, 6924–6928.
Zahler AM, Lane WS, Stolk JA & Roth MB. SR proteins: a conserved family of pre-mRNA splicing factors, Genes Dev, 1992, 6, 837–847.
Zahler AM, Neugebauer KM, Lane WS & Roth MB. Distinct functions of SR proteins in alternative pre-mRNA splicing, Science, 1993, 260, 219–222.
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