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Review
. 2004 Apr;24(8):3069-76.
doi: 10.1128/MCB.24.8.3069-3076.2004.

Nucleocytoplasmic transport: integrating mRNA production and turnover with export through the nuclear pore

Christian Dimaano  1 , Katharine S Ullman
Affiliations
Review

Nucleocytoplasmic transport: integrating mRNA production and turnover with export through the nuclear pore

Christian Dimaano et al. Mol Cell Biol. 2004 Apr.
No abstract available

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Figures

FIG. 1.
FIG. 1.
Interconnections between steps in mRNA biogenesis. A schematic illustration of mRNA biogenesis is depicted, with the proposed times of recruitment and functions for specific proteins indicated in the boxes. (1) Transcription. Much evidence points to cotranscriptional loading of factors involved in RNA processing, export, and quality control to the nascent transcript. The mobile pore proteins, Nup153 and Nup98, are candidates (indicated in red text) for loading onto mRNA early in its biogenesis, although this is yet to be demonstrated. RNAPII, RNA polymerase II. (2) Splicing. The splicing factor UAP56 interacts with REF, which is one of a group of proteins referred to as the EJC that is deposited on mRNA in conjunction with splicing. Loading of certain transport factors, such as REF, can also occur independent of splicing as a part of TREX or if the RNA is sufficiently long. (3) Remodeling and export. NXF1-p15 is recruited to the mRNA via protein-protein interactions, readying export-competent mRNA for mobilization out of the nucleus. At this step, other proteins, such as Gle1, RAE1, Trn-2 (transportin-2), and TREX components, are also thought to function. Certain hnRNPs and EJC components are shed from the mRNP prior to export, and proper mRNP formation appears to be monitored at this stage by the exosome. Specific pore proteins, or Nups, are implicated in moving mRNA cargo through the pore (Fig. 2). Although loaded onto the transcript early in biogenesis, Dbp5 may play a late role in remodeling and/or moving the mRNP complex. (4) Cytoplasmic function. Factors remaining on the mRNA, such as Y14 and Magoh, influence translation and localization of mature mRNPs.
FIG. 2.
FIG. 2.
Distribution and dynamics of pore proteins and associated factors implicated in mRNA export. Nup153 and Nup98 are both dynamically associated with the nuclear pore in a manner dependent on ongoing transcription. However, in the case of Nup153, there is also evidence for a stable population, which is schematically illustrated here proximal to the inner nuclear membrane. The presence of distinct populations of Nup153 is consistent with epitope exposure of this protein: different regions are exposed at the distal and proximal ends of the pore basket. An extended conformation of Nup153 at the pore is an alternative explanation for epitope distribution. Regardless of exactly how Nup153 is arranged at the pore basket, there is evidence that the C-terminal region of this pore protein can extend into the cytoplasm, although Nup153 does not appear to be released from this face of the pore. In contrast, Nup98 exists in equilibrium with a cytoplasmic pool and is known to interact with components of both sides of the pore. RAE1/Gle2 is a partner protein of Nup98. Both Nup153 and Nup98 associate with the Nup107-160 complex, a stable component of the pore. Tpr is also a component of the nuclear pore basket and relies on interaction with Nup153 for correct localization. CAN/Nup214 is localized to fibrils extending from the cytoplasmic ring of the pore and is a docking site for the dynamic DEAD box helicase, Dbp5.
See this image and copyright information in PMC

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