51
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Abstract
Export of mRNA through nuclear pore complexes (NPC) is preceded by multiple and well coordinated processing steps, resulting in the formation of an export competent ribonucleoprotein complex (mRNP). Numerous factors involved in the translocation of the mRNP through the NPC and its release into the cytoplasm have been isolated mainly through genetic approaches in yeast, and putative functional homologues have been identified in metazoan systems. Understanding the mechanism of mRNA export relies, in part, on the functional characterization of these factors and the establishment of a complete network of molecular interactions. Here we summarize recent progress in the characterization of yeast and mammalian components implicated in the export of an mRNA from the nucleus to the cytoplasm.
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Affiliation(s)
- D Zenklusen
- Institute of Microbiology, Centre Hospitalier Universitaire Vaudois, 44, rue du Bugnon, 1011, Lausanne, Switzerland
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52
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Wang X, Babu JR, Harden JM, Jablonski SA, Gazi MH, Lingle WL, de Groen PC, Yen TJ, van Deursen JM. The mitotic checkpoint protein hBUB3 and the mRNA export factor hRAE1 interact with GLE2p-binding sequence (GLEBS)-containing proteins. J Biol Chem 2001; 276:26559-67. [PMID: 11352911 DOI: 10.1074/jbc.m101083200] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mRNA export factor RAE1 (also called GLE2) and the mitotic checkpoint protein BUB3 share extensive sequence homology in yeast as well as higher eukaryotes, although the biological relevance of their similarity is unclear. Previous work in HeLa cells has shown that human (h)RAE1 binds the nuclear pore complex protein hNUP98 via a short NUP98 motif called GLEBS (for GLE2p-binding sequence). Here we report that the two known binding partners of hBUB3, the mitotic checkpoint proteins hBUB1 and hBUBR1, both carry a region with remarkable similarity to the GLEBS motif of hNUP98. We show that the GLEBS-like motifs of mouse (m)BUB1 and mBUBR1 are sufficient for mBUB3 binding. mBUB3 lacks affinity for the hNUP98 GLEBS, demonstrating its binding specificity for GLEBS motifs of mitotic checkpoint proteins. Interestingly, mRAE1 does not exclusively bind to the GLEBS motif of hNUP98 and can cross-interact with the mBUB1 GLEBS. We show that full-length RAE1 and BUB1 proteins interact in mammalian cells and accumulate both at the kinetochores of prometaphase chromosomes. Our findings demonstrate that GLEBS motifs reside in mammalian nucleoporins and mitotic checkpoint proteins and apparently serve as specific binding sites for either BUB3, RAE1, or both.
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Affiliation(s)
- X Wang
- Department of Pediatrics and Adolescent Medicine, Mayo Clinic, Rochester, Minnesota 55905, USA
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53
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Davies E, Stankovic B, Azama K, Shibata K, Abe S. Novel components of the plant cytoskeleton: a beginning to plant 'cytomics'. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2001; 160:185-196. [PMID: 11164590 DOI: 10.1016/s0168-9452(00)00365-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The bulk of our knowledge concerning the plant cytoskeleton has come primarily from the use of techniques and probes derived from animal research. However, in comparison with animal tissues, relatively few plant cytoskeleton proteins have been identified. We presume this is not because the plant cytoskeleton is really made up of such few proteins, but rather that only rarely have attempts been made to identify plant-specific cytoskeleton proteins, using plant-specific methods. Here we outline methods that we have developed both for the isolation and identification of novel cytoskeleton proteins as well as for the visualization of novel filamentous structures in plant cells, and we describe several novel cytoskeleton proteins and two novel cytoskeleton structures, 'nanofilaments' and 'nanotubules'. We postulate that use of such approaches will lead to a rapid expansion of our knowledge of the plant cytoskeleton.
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Affiliation(s)
- E Davies
- Botany Department, North Carolina State University, 27695-7612, Raleigh, NC, USA
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54
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Yoon JH, Love DC, Guhathakurta A, Hanover JA, Dhar R. Mex67p of Schizosaccharomyces pombe interacts with Rae1p in mediating mRNA export. Mol Cell Biol 2000; 20:8767-82. [PMID: 11073978 PMCID: PMC86506 DOI: 10.1128/mcb.20.23.8767-8782.2000] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We identified the Schizosaccharomyces pombe mex67 gene (spmex67) as a multicopy suppressor of rae1-167 nup184-1 synthetic lethality and the rae1-167 ts mutation. spMex67p, a 596-amino-acid-long protein, has considerable sequence similarity to the Saccharomyces cerevisiae Mex67p (scMex67p) and human Tap. In contrast to scMEX67, spmex67 is essential for neither growth nor nuclear export of mRNA. However, an spmex67 null mutation (Deltamex67) is synthetically lethal with the rae1-167 mutation and accumulates poly(A)(+) RNA in the nucleus. We identified a central region (149 to 505 amino acids) within spMex67p that associates with a complex containing Rae1p that complements growth and mRNA export defects of the rae1-167 Deltamex67 synthetic lethality. This region is devoid of RNA-binding, N-terminal nuclear localization, and the C-terminal nuclear pore complex-targeting regions. The (149-505)-green fluorescent protein (GFP) fusion is found diffused throughout the cell. Overexpression of spMex67p inhibits growth and mRNA export and results in the redistribution of the diffused localization of the (149-505)-GFP fusion to the nucleus and the nuclear periphery. These results suggest that spMex67p competes for essential mRNA export factor(s). Finally, we propose that the 149-505 region of spMex67p could act as an accessory factor in Rae1p-dependent transport and that spMex67p participates at various common steps with Rae1p export complexes in promoting the export of mRNA.
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Affiliation(s)
- J H Yoon
- Basic Research Laboratory, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
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55
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Herold A, Suyama M, Rodrigues JP, Braun IC, Kutay U, Carmo-Fonseca M, Bork P, Izaurralde E. TAP (NXF1) belongs to a multigene family of putative RNA export factors with a conserved modular architecture. Mol Cell Biol 2000; 20:8996-9008. [PMID: 11073998 PMCID: PMC86553 DOI: 10.1128/mcb.20.23.8996-9008.2000] [Citation(s) in RCA: 165] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2000] [Accepted: 09/06/2000] [Indexed: 11/20/2022] Open
Abstract
Vertebrate TAP (also called NXF1) and its yeast orthologue, Mex67p, have been implicated in the export of mRNAs from the nucleus. The TAP protein includes a noncanonical RNP-type RNA binding domain, four leucine-rich repeats, an NTF2-like domain that allows heterodimerization with p15 (also called NXT1), and a ubiquitin-associated domain that mediates the interaction with nucleoporins. Here we show that TAP belongs to an evolutionarily conserved family of proteins that has more than one member in higher eukaryotes. Not only the overall domain organization but also residues important for p15 and nucleoporin interaction are conserved in most family members. We characterize two of four human TAP homologues and show that one of them, NXF2, binds RNA, localizes to the nuclear envelope, and exhibits RNA export activity. NXF3, which does not bind RNA or localize to the nuclear rim, has no RNA export activity. Database searches revealed that although only one p15 (nxt) gene is present in the Drosophila melanogaster and Caenorhabditis elegans genomes, there is at least one additional p15 homologue (p15-2 [also called NXT2]) encoded by the human genome. Both human p15 homologues bind TAP, NXF2, and NXF3. Together, our results indicate that the TAP-p15 mRNA export pathway has diversified in higher eukaryotes compared to yeast, perhaps reflecting a greater substrate complexity.
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Affiliation(s)
- A Herold
- European Molecular Biology Laboratory, D-69117 Heidelberg, Germany
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56
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Sabri N, Visa N. The Ct-RAE1 protein interacts with Balbiani ring RNP particles at the nuclear pore. RNA (NEW YORK, N.Y.) 2000; 6:1597-1609. [PMID: 11105759 PMCID: PMC1370029 DOI: 10.1017/s1355838200001138] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
RAE1 is an evolutionarily conserved protein that associates with both mRNPs and nucleoporins, and may bridge the interaction between mRNP export cargoes and the nuclear pore complex (NPC). However, the mechanism by which RAE1 functions in mRNA export is still unknown and the time point at which RAE1 interacts with the exported RNP has not been directly investigated. Here we have addressed this question in the Balbiani ring (BR) system of Chironomus tentans using immunoelectron microscopy. The RAE1 protein of C. tentans, Ct-RAE1, is 70% identical to human RAE1/mrnp41 (hRAE1) and is recognized by antibodies raised against hRAE1. As in vertebrate cells, Ct-RAE1 is concentrated at the nuclear envelope and also dispersed throughout the nuclear interior. Here we show that Ct-RAE1 does not bind to the BR particle either cotranscriptionally or in the nucleoplasm. Instead, the interaction between Ct-RAE1 and the exported BR particle occurs at the NPC. Moreover, the localization of Ct-RAE1 at the NPC is correlated with the presence of an exported RNP in the NPC. Finally, the anti-RAE1 antibody does not label the cytoplasmic side of BR particles in transit through the central channel, which indicates that Ct-RAE1 either remains anchored at the nuclear side of the NPC during translocation of the RNP through the central channel or becomes transiently associated with the RNP but is rapidly released into the cytoplasm.
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Affiliation(s)
- N Sabri
- Department of Molecular Genome Research, University of Stockholm, Sweden
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57
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Sträßer K, Baßler J, Hurt E. Binding of the Mex67p/Mtr2p heterodimer to FXFG, GLFG, and FG repeat nucleoporins is essential for nuclear mRNA export. J Cell Biol 2000; 150:695-706. [PMID: 10952996 PMCID: PMC2175290 DOI: 10.1083/jcb.150.4.695] [Citation(s) in RCA: 180] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
It is not known how Mex67p and Mtr2p, which form a heterodimer essential for mRNA export, transport mRNPs through the nuclear pore. Here, we show that the Mex67p/Mtr2p complex binds to all of the repeat types (GLFG, FXFG, and FG) found in nucleoporins. For this interaction, complex formation between Mex67p and Mtr2p has to occur. MEX67 and MTR2 also genetically interact with different types of repeat nucleoporins, such as Nup116p, Nup159p, Nsp1p, and Rip1p/Nup40p. These data suggest a model in which nuclear mRNA export requires the Mex67p/Mtr2p heterodimeric complex to directly contact several repeat nucleoporins, organized in different nuclear pore complex subcomplexes, as it carries the mRNP cargo through the nuclear pore.
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Affiliation(s)
- Katja Sträßer
- BZH, Biochemie-Zentrum Heidelberg, D-69120 Heidelberg, Germany
| | - Jochen Baßler
- BZH, Biochemie-Zentrum Heidelberg, D-69120 Heidelberg, Germany
| | - Ed Hurt
- BZH, Biochemie-Zentrum Heidelberg, D-69120 Heidelberg, Germany
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58
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Bailer SM, Balduf C, Katahira J, Podtelejnikov A, Rollenhagen C, Mann M, Pante N, Hurt E. Nup116p associates with the Nup82p-Nsp1p-Nup159p nucleoporin complex. J Biol Chem 2000; 275:23540-8. [PMID: 10801828 DOI: 10.1074/jbc.m001963200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nup116p is a GLFG nucleoporin involved in RNA export processes. We show here that Nup116p physically interacts with the Nup82p-Nsp1p-Nup159p nuclear pore subcomplex, which plays a central role in nuclear mRNA export. For this association, a sequence within the C-terminal domain of Nup116p that includes the conserved nucleoporin RNA-binding motif was sufficient and necessary. Consistent with this biochemical interaction, protein A-Nup116p and the protein A-tagged Nup116p C-terminal domain, like the members of the Nup82p complex, localized to the cytoplasmic side of the nuclear pore complex, as revealed by immunogold labeling. Finally, synthetic lethal interactions were found between mutant alleles of NUP116 and all members of the Nup82p complex. Thus, Nup116p consists of three independent functional domains: 1) the C-terminal part interacts with the Nup82p complex; 2) the Gle2p-binding sequence interacts with Gle2p/Rae1p; and 3) the GLFG domain interacts with shuttling transport receptors such as karyopherin-beta family members.
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Affiliation(s)
- S M Bailer
- Biochemie-Zentrum Heidelberg, Im Neuenheimer Feld 328, D-69120 Heidelberg, Germany
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59
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Abstract
In eukaryotic cells, the nuclear membrane creates a barrier between the nucleus and the cytoplasm. Whereas RNA synthesis occurs in the nucleus, they mostly function in the cytoplasm; thus export of RNA molecules from the nucleus to the cytoplasm is indispensable for normal function of the cells. The molecular mechanisms involved in each kind of cellular RNA export is gradually understood. The focus of this review will be mRNA export. mRNAs are multiformed. In order to ensure that this variety of mRNA molecules are all exported, cells are probably equipped with multiple export pathways. A number of proteins is predicted to be involved in mRNA export. Ascertaining which proteins play crucial roles in the pathways is the key point in the study of mRNA export.
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Affiliation(s)
- M C Siomi
- Institute for Genome Research, University of Tokushima, Japan.
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60
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Affiliation(s)
- B R Cullen
- Howard Hughes Medical Institute and Department of Genetics, Duke University Medical Center, Durham, North Carolina 27710, USA.
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61
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Ryan KJ, Wente SR. The nuclear pore complex: a protein machine bridging the nucleus and cytoplasm. Curr Opin Cell Biol 2000; 12:361-71. [PMID: 10801463 DOI: 10.1016/s0955-0674(00)00101-0] [Citation(s) in RCA: 196] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Compositional analysis of nuclear pore complexes (NPCs) is nearing completion, and efforts are now focused on understanding how these protein machines work. Recent analysis of soluble transport factor interactions with NPC proteins reveals distinct and overlapping pathways for movement between the nucleus and cytoplasm. New fluorescence- and microscopy-based strategies have been used to monitor the pathway of NPC assembly and to reveal the dynamics of the NPC during transport.
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Affiliation(s)
- K J Ryan
- Department of Cell Biology and Physiology, Washington University School of Medicine, Box 8228, St Louis, MO 63110, USA. kryan@cellbio. wustl.edu
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62
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Stutz F, Bachi A, Doerks T, Braun IC, Séraphin B, Wilm M, Bork P, Izaurralde E. REF, an evolutionary conserved family of hnRNP-like proteins, interacts with TAP/Mex67p and participates in mRNA nuclear export. RNA (NEW YORK, N.Y.) 2000; 6:638-650. [PMID: 10786854 PMCID: PMC1369944 DOI: 10.1017/s1355838200000078] [Citation(s) in RCA: 299] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Vertebrate TAP and its yeast ortholog Mex67p are involved in the export of messenger RNAs from the nucleus. TAP has also been implicated in the export of simian type D viral RNAs bearing the constitutive transport element (CTE). Although TAP directly interacts with CTE-bearing RNAs, the mode of interaction of TAP/Mex67p with cellular mRNAs is different from that with the CTE RNA and is likely to be mediated by protein-protein interactions. Here we show that Mex67p directly interacts with Yra1p, an essential yeast hnRNP-like protein. This interaction is evolutionarily conserved as Yra1p also interacts with TAP. Conditional expression in yeast cells implicates Yra1 p in the export of cellular mRNAs. Database searches revealed that Yra1p belongs to an evolutionarily conserved family of hnRNP-like proteins having more than one member in Mus musculus, Xenopus laevis, Caenorhabditis elegans, and Schizosaccharomyces pombe and at least one member in several species including plants. The murine members of the family directly interact with TAP. Because members of this protein family are characterized by the presence of one RNP-motif RNA-binding domain and exhibit RNA-binding activity, we called these proteins REF-bps for RNA and export factor binding proteins. Thus, Yra1p and members of the REF family of hnRNP-like proteins may facilitate the interaction of TAP/Mex67p with cellular mRNAs.
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Affiliation(s)
- F Stutz
- Institute of Microbiology, Lausanne, Switzerland
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63
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Iborra FJ, Jackson DA, Cook PR. The path of RNA through nuclear pores: apparent entry from the sides into specialized pores. J Cell Sci 2000; 113 Pt 2:291-302. [PMID: 10633080 DOI: 10.1242/jcs.113.2.291] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The path that RNA takes through nuclear pores was mapped using two high-resolution techniques. Unexpectedly, no RNA in HL60 cells was detected by immunogold labelling in the central axis of the pore complex on its way to the transporter at the nuclear membrane; instead, it was distributed around the sides, apparently entering just before the membrane. In rat liver nuclei, poly(A)(+) RNA, hnRNPs A1 and C, mrnp 41, ASF, and a phosphorylated subset of SR proteins were also distributed like mRNA, as were various transport factors and their cargoes (NTF2, Ran, RCC1, karyopherin (beta), Rch1, transportin (alpha), m(2,2,7)-trimethylG). Many pores were associated with particular transport factors/cargoes to the exclusion of others; some were associated with poly(A)(+) RNA or phosphorylated SR proteins (but not NTF2), others with NTF2 (but not poly(A)(+) RNA or the SR proteins). Electron spectroscopic imaging confirmed these results. Some pores contained phosphorus-rich RNA apparently entering from the sides; others lacked any phosphorus, and were surrounded by a ribosome-free zone in the cytoplasm. The results also suggest that pores have different functional zones where SR proteins are dephosphorylated, and where hnRNP C is removed from messages.
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Affiliation(s)
- F J Iborra
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK
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64
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Bachi A, Braun IC, Rodrigues JP, Panté N, Ribbeck K, von Kobbe C, Kutay U, Wilm M, Görlich D, Carmo-Fonseca M, Izaurralde E. The C-terminal domain of TAP interacts with the nuclear pore complex and promotes export of specific CTE-bearing RNA substrates. RNA (NEW YORK, N.Y.) 2000; 6:136-58. [PMID: 10668806 PMCID: PMC1369901 DOI: 10.1017/s1355838200991994] [Citation(s) in RCA: 270] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Messenger RNAs are exported from the nucleus as large ribonucleoprotein complexes (mRNPs). To date, proteins implicated in this process include TAP/Mex67p and RAE1/Gle2p and are distinct from the nuclear transport receptors of the beta-related, Ran-binding protein family. Mex67p is essential for mRNA export in yeast. Its vertebrate homolog TAP has been implicated in the export of cellular mRNAs and of simian type D viral RNAs bearing the constitutive transport element (CTE). Here we show that TAP is predominantly localized in the nucleoplasm and at both the nucleoplasmic and cytoplasmic faces of the nuclear pore complex (NPC). TAP interacts with multiple components of the NPC including the nucleoporins CAN, Nup98, Nup153, p62, and with three major NPC subcomplexes. The nucleoporin-binding domain of TAP comprises residues 508-619. In HeLa cells, this domain is necessary and sufficient to target GFP-TAP fusions to the nuclear rim. Moreover, the isolated domain strongly competes multiple export pathways in vivo, probably by blocking binding sites on the NPC that are shared with other transport receptors. Microinjection experiments implicate this domain in the export of specific CTE-containing RNAs. Finally, we show that TAP interacts with transportin and with two proteins implicated in the export of cellular mRNAs: RAE1/hGle2 and E1B-AP5. The interaction of TAP with nucleoporins, its direct binding to the CTE RNA, and its association with two mRNP binding proteins suggest that TAP is an RNA export mediator that may bridge the interaction between specific RNP export substrates and the NPC.
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Affiliation(s)
- A Bachi
- European Molecular Biology Laboratory, Heidelberg, Germany
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65
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Abstract
The compartmentation of eukaryotic cells requires all nuclear proteins to be imported from the cytoplasm, whereas, for example, transfer RNAs, messenger RNAs, and ribosomes are made in the nucleus and need to be exported to the cytoplasm. Nuclear import and export proceed through nuclear pore complexes and can occur along a great number of distinct pathways, many of which are mediated by importin beta-related nuclear transport receptors. These receptors shuttle between nucleus and cytoplasm, and they bind transport substrates either directly or via adapter molecules. They all cooperate with the RanGTPase system to regulate the interactions with their cargoes. Another focus of our review is nuclear export of messenger RNA, which apparently largely relies on export mediators distinct from importin beta-related factors. We discuss mechanistic aspects and the energetics of transport receptor function and describe a number of pathways in detail.
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Affiliation(s)
- D Görlich
- Zentrum für Molekulare Biologie, Universität Heidelberg, Federal Republic of Germany.
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66
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Affiliation(s)
- S Nakielny
- Howard Hughes Medical Institute and Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia 19104-6148, USA
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67
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Luo MJ, Reed R. Splicing is required for rapid and efficient mRNA export in metazoans. Proc Natl Acad Sci U S A 1999; 96:14937-42. [PMID: 10611316 PMCID: PMC24751 DOI: 10.1073/pnas.96.26.14937] [Citation(s) in RCA: 296] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Pre-mRNA splicing is among the last known nuclear events before export of mature mRNA to the cytoplasm. At present, it is not known whether splicing and mRNA export are biochemically coupled processes. In this study, we have injected pre-mRNAs containing a single intron or the same mRNAs lacking an intron (Deltai-mRNAs) into Xenopus oocyte nuclei. We find that the spliced mRNAs are exported much more rapidly and efficiently than the identical Deltai-mRNAs. Moreover, competition studies using excess Deltai-mRNA indicate that different factor(s) are involved in the inefficient export of Deltai-mRNA vs. the efficient export of spliced mRNA. Consistent with this conclusion, spliced mRNA and Deltai-mRNA, though identical in sequence, are assembled into different messenger ribonucleoprotein particles (mRNP) in vitro. Strikingly, the mRNA in the spliced mRNP, but not in the Deltai-mRNP, is exported rapidly and efficiently. We conclude that splicing generates a specific nucleoprotein complex that targets mRNA for export. Our results, revealing a link between splicing and efficient mRNA export, may explain the reports that an intron is required for efficient expression of many protein-coding genes in metazoans.
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Affiliation(s)
- M J Luo
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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68
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Abstract
Eukaryotic cells massively exchange macromolecules (proteins and RNAs) between the nucleus and cytoplasm through the nuclear pore complexes. Whereas a mechanistic picture emerges of how proteins are imported into and exported from the nucleus, less is known about nuclear exit of the different classes of RNAs. However, the yeast Saccharomyces cerevisiae offers an experimental system to study nuclear RNA export in vivo and thus to genetically dissect the different RNA export machineries. In this review, we summarize our current knowledge and recent progress in identifying components involved in nuclear RNA export in yeast.
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Affiliation(s)
- K Strässer
- BZH, Biochemie-Zentrum Heidelberg, Germany
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69
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Stuger R, Ranostaj S, Materna T, Forreiter C. Messenger RNA-binding properties of nonpolysomal ribonucleoproteins from heat-stressed tomato cells. PLANT PHYSIOLOGY 1999; 120:23-32. [PMID: 10318680 PMCID: PMC59255 DOI: 10.1104/pp.120.1.23] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/1998] [Accepted: 01/31/1999] [Indexed: 05/23/2023]
Abstract
Most cells experiencing heat stress reprogram their translational machinery to favor the synthesis of heat-stress proteins. Translation of other transcripts is almost completely repressed, but most untranslated messengers are not degraded. In contrast to yeast, Drosophila melanogaster, and HeLa cells, plant cells store repressed messengers in cytoplasmic nonpolysomal ribonucleoproteins (RNPs). To follow the fate of untranslated transcripts, we studied protein composition, mRNA content, and RNA-binding properties of nonpolysomal RNPs from heat-stressed tomato (Lycopersicon peruvianum) cells. Contrary to the selective interaction in vivo, RNPs isolated from tomato cells bound both stress-induced and repressed messengers, suggesting that the selection mechanism resides elsewhere. This binding was independent of a cap or a poly(A) tail. The possible role of proteasomes and heat-stress granules (HSGs) in mRNA storage is a topic of debate. We found in vitro messenger-RNA-binding activity in messenger RNP fractions free of C2-subunit-containing proteasomes and HSGs. In addition, mRNAs introduced into tobacco (Nicotiana plumbaginifolia) protoplasts were found in the cytoplasm but were not associated with HSGs.
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Affiliation(s)
- R Stuger
- Department of Molecular Cell Biology, Goethe University, Marie Curie Strasse 9, 60439 Frankfurt am Main, Germany
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70
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Pritchard CE, Fornerod M, Kasper LH, van Deursen JM. RAE1 is a shuttling mRNA export factor that binds to a GLEBS-like NUP98 motif at the nuclear pore complex through multiple domains. J Cell Biol 1999; 145:237-54. [PMID: 10209021 PMCID: PMC2133102 DOI: 10.1083/jcb.145.2.237] [Citation(s) in RCA: 194] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Gle2p is implicated in nuclear export of poly(A)+ RNA and nuclear pore complex (NPC) structure and distribution in Saccharomyces cerevisiae. Gle2p is anchored at the nuclear envelope (NE) via a short Gle2p-binding motif within Nup116p called GLEBS. The molecular mechanism by which Gle2p and the Gle2p-Nup116p interaction function in mRNA export is unknown. Here we show that RAE1, the mammalian homologue of Gle2p, binds to a GLEBS-like NUP98 motif at the NPC through multiple domains that include WD-repeats and a COOH-terminal non-WD-repeat extension. This interaction is direct, as evidenced by in vitro binding studies and chemical cross-linking. Microinjection experiments performed in Xenopus laevis oocytes demonstrate that RAE1 shuttles between the nucleus and the cytoplasm and is exported from the nucleus in a temperature-dependent and RanGTP-independent manner. Docking of RAE1 to the NE is highly dependent on new mRNA synthesis. Overexpression of the GLEBS-like motif also inhibits NE binding of RAE1 and induces nuclear accumulation of poly(A)+ RNA. Both effects are abrogated either by the introduction of point mutations in the GLEBS-like motif or by overexpression of RAE1, indicating a direct role for RAE1 and the NUP98-RAE1 interaction in mRNA export. Together, our data suggest that RAE1 is a shuttling transport factor that directly contributes to nuclear export of mRNAs through its ability to anchor to a specific NUP98 motif at the NPC.
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Affiliation(s)
- C E Pritchard
- Department of Genetics, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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71
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72
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Matsuoka Y, Takagi M, Ban T, Miyazaki M, Yamamoto T, Kondo Y, Yoneda Y. Identification and characterization of nuclear pore subcomplexes in mitotic extract of human somatic cells. Biochem Biophys Res Commun 1999; 254:417-23. [PMID: 9918853 DOI: 10.1006/bbrc.1998.9953] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
In higher eukaryotic cells, it is generally thought that nuclear pore complex disassembles at the beginning of mitosis and reassembles at the end. Using a monoclonal antibody that recognizes nuclear pore antigens, we found that, at mitosis of mammalian somatic Hela cells, the nuclear pore complex disassembles into at least three subcomplexes, termed subcomplexes A, B and C (molecular mass; 2 MDa<, approximately 660 kDa, and approximately 440 kDa, respectively). The direct partial amino acid sequencing of the components of these subcomplexes indicates that the A subcomplex contains CAN/Nup214/p250 and p62 and the B subcomplex also contains p62, indicating that p62 is contained in two different subcomplexes. Subcomplex C was shown to consist of Nup98 and human RAE1, a human homolog of yeast Rae1p/Gle2p. Since Nup98 and Rae1p/Gle2p have been reported to be involved in mRNA export, this suggests that some of the mitotic subcomplex may be formed by functionally related proteins.
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Affiliation(s)
- Y Matsuoka
- Department of Anatomy and Cell Biology, Osaka University Medical School, 2-2 Yamada-oka, Suita, Osaka, 565-0871, Japan
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73
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Affiliation(s)
- F Stutz
- Institut de Microbiologie, Centre Hospitalier Universitaire Vaudois, 1011 Lausanne, Switzerland.
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74
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Morales CR, Wu XQ, Hecht NB. The DNA/RNA-binding protein, TB-RBP, moves from the nucleus to the cytoplasm and through intercellular bridges in male germ cells. Dev Biol 1998; 201:113-23. [PMID: 9733578 DOI: 10.1006/dbio.1998.8967] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The genetically haploid spermatids are functionally diploid as a result of the sharing of gene products through their intercellular bridges. This movement of molecules among haploid cells is crucial for the production of spermatozoa since numerous essential proteins are encoded on sex chromosomes. Testis-brain RNA-binding protein (TB-RBP) is a single-stranded DNA- and RNA-binding protein prominent in the nuclei and cytoplasm of specific stages of differentiating male germ cells. Here we present evidence that TB-RBP moves from the nucleus to the cytoplasm and through intercellular bridges of male germ cells. Based on its RNA-binding capabilities, we propose a role for TB-RBP in the distribution of equal amounts of mRNAs in haploid male germ cells.
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Affiliation(s)
- C R Morales
- Department of Anatomy and Cell Biology, Mc Gill University, Montreal, Canada
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75
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Wu L, Osmani SA, Mirabito PM. A role for NIMA in the nuclear localization of cyclin B in Aspergillus nidulans. J Cell Biol 1998; 141:1575-87. [PMID: 9647650 PMCID: PMC2133011 DOI: 10.1083/jcb.141.7.1575] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/1997] [Revised: 05/08/1998] [Indexed: 02/08/2023] Open
Abstract
NIMA promotes entry into mitosis in late G2 by some mechanism that is after activation of the Aspergillus nidulans G2 cyclin-dependent kinase, NIMXCDC2/NIMECyclin B. Here we present two independent lines of evidence which indicate that this mechanism involves control of NIMXCDC2/NIMECyclin B localization. First, we found that NIMECyclin B localized to the nucleus and the nucleus-associated organelle, the spindle pole body, in a NIMA-dependent manner. Analysis of cells from asynchronous cultures, synchronous cultures, and cultures arrested in S or G2 showed that NIMECyclin B was predominantly nuclear during interphase, with maximal nuclear accumulation in late G2. NIMXCDC2 colocalized with NIMECyclin B in G2 cells. Although inactivation of NIMA using either the nimA1 or nimA5 temperature-sensitive mutations blocked cells in G2, NIMXCDC2/NIMECyclin B localization was predominantly cytoplasmic rather than nuclear. Second, we found that nimA interacts genetically with sonA, which is a homologue of the yeast nucleocytoplasmic transporter GLE2/RAE1. Mutations in sonA were identified as allele-specific suppressors of nimA1. The sonA1 suppressor alleviated the nuclear division and NIMECyclin B localization defects of nimA1 cells without markedly increasing NIMXCDC2 or NIMA kinase activity. These results indicate that NIMA promotes the nuclear localization of the NIMXCDC2/ NIMECyclin B complex, by a process involving SONA. This mechanism may be involved in coordinating the functions of NIMXCDC2 and NIMA in the regulation of mitosis.
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Affiliation(s)
- L Wu
- Henry Hood Research Program, Weis Center for Research, Pennsylvania State University College of Medicine, Danville, Pennsylvania 17822-2617, USA
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76
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Bailer SM, Siniossoglou S, Podtelejnikov A, Hellwig A, Mann M, Hurt E. Nup116p and nup100p are interchangeable through a conserved motif which constitutes a docking site for the mRNA transport factor gle2p. EMBO J 1998; 17:1107-19. [PMID: 9463388 PMCID: PMC1170459 DOI: 10.1093/emboj/17.4.1107] [Citation(s) in RCA: 114] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Nup116p and Nup100p are highly related yeast GLFG nucleoporins, but only Nup116p is stoichiometrically bound to Gle2p, a previously identified mRNA export factor. A short Gle2p-binding sequence within Nup116p (GLEBS; residues 110-166) is sufficient and necessary to anchor Gle2p at the nuclear pores, whereas the carboxy-terminal domain of Nup116p mediates its own nuclear pore complex (NPC) association. The GLEBS is evolutionarily conserved and found in rat/Xenopus Nup98 and an uncharacterized Caenorhabditis elegans ORF, but is absent from Nup100p. When the GLEBS is deleted from Nup116p, Gle2p dissociates from the nuclear envelope and clusters of herniated nuclear pores form. When the GLEBS is inserted into Nup100p, Nup100p-GLEBS complements both the thermosensitive and NPC-herniated phenotype of nup116- cells, and Gle2p is retargeted concomitantly to the NPCs. Thus, the in vivo function of Gle2p is strictly coupled to the short GLEBS within Nup116p which links this putative mRNA transport factor to the nuclear pores.
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Affiliation(s)
- S M Bailer
- University of Heidelberg, Biochemie-Zentrum Heidelberg (BZH), Germany.
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77
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Pemberton LF, Rosenblum JS, Blobel G. A distinct and parallel pathway for the nuclear import of an mRNA-binding protein. J Cell Biol 1997; 139:1645-53. [PMID: 9412460 PMCID: PMC2132632 DOI: 10.1083/jcb.139.7.1645] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Three independent pathways of nuclear import have so far been identified in yeast, each mediated by cognate nuclear transport factors, or karyopherins. Here we have characterized a new pathway to the nucleus, mediated by Mtr10p, a protein first identified in a screen for strains defective in polyadenylated RNA export. Mtr10p is shown to be responsible for the nuclear import of the shuttling mRNA-binding protein Npl3p. A complex of Mtr10p and Npl3p was detected in cytosol, and deletion of Mtr10p was shown to lead to the mislocalization of nuclear Npl3p to the cytoplasm, correlating with a block in import. Mtr10p bound peptide repeat-containing nucleoporins and Ran, suggesting that this import pathway involves a docking step at the nuclear pore complex and is Ran dependent. This pathway of Npl3p import is distinct and does not appear to overlap with another known import pathway for an mRNA-binding protein. Thus, at least two parallel pathways function in the import of mRNA-binding proteins, suggesting the need for the coordination of these pathways.
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Affiliation(s)
- L F Pemberton
- Laboratory of Cell Biology, Howard Hughes Medical Institute, The Rockefeller University, New York 10021, USA
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