Exportin

IMPORTINS EXPORTINS ARE INVOLVED IN TRANSPORT OF MACROMOLECULES IN OUT OF THE NUCLEUS... 

Binding of substrates to exportins is regulated in a converse manner to importins. Exportins bind their cargoes preferentially in the nucleus, forming a trimeric cargo exportin Ran GTP complex [142]. This trimeric complex is then transferred to the cytoplasm where Ran GTP is converted to Ran GDP. This results in Ran s dissociation from the complex, allowing the exportin to release its substrate, re-enter the nucleus, and to start the next export cycle. 

RRE (RNA signal) Rev responsive element 234nt segment of env in HIV-1 Exportin 1/Rev... 

Yi R, Qin Y, Macara IG et al. Exportin-5 mediates the nuclear export of pre-microRNAs and short hairpin RNAs. Genes Dev 2003 17 3011-3016. 

A functional NES comprised of hydrophobic leucine and isoleucine residues has been identified in the IVR domain of Keapl [Velichkova and Hasson, 2005], Mutation of the hydrophobic residues as well as leptomycin B (LMB) treatment, which inactivates Crml/exportin, resulted in nuclear accumulation of both Nrf2 and Keapl. It was further demonstrated that the NES in Keapl is required for termination of Nrf2/ARE signaling, and the Nrf2/Keapl complex does not bind to the ARE [Sun et al., 2007], Conversely, in another report the subcellular distribution of endogenous Keapl was essentially similar before and after LMB treatment [Watai et al., 2007], This discrepancy could possibly be... 

Figure 12.2 Model for importin-mediated nuclear import and export. NLS-containing proteins in the cytoplasm bind to importin family members in the cytoplasm and are translocated through the NPC. Once inside the nucleus, Ran-GTP interacts with the importin-cargo complex to facilitate complex dissociation. Similarly, proteins to be exported from the nucleus interact with one of the exportins, but in contrast to the case with importins, assembly of this complex is promoted by Ran-GTP. As the complex, presumably with Ran-GTP bound, enters the cytoplasm, the GTP is hydrolyzed to GDP, which induces the release of the cargo from exportin.

Because the export machinery selectively binds transport-competent mRNPs, i.e., mRNAs associated with the appropriate nuclear proteins, the diffusion-based model for intranuclear RNA movement provides an additional checkpoint for gene expression at the level of mRNA export. This type of control has been demonstrated for tRNA export only mature tRNAs are transported to the cytoplasm because incompletely processed tRNAs do not efficiently bind to exportin-t, the tRNA-specific export receptor. 

According to the direction in which they carry a cargo, the receptors are classified as importins or exportins. Importins bind their import substrates in the presence of RanGDP in the cytoplasm. Upon... 

Arts, G.J., Kuersten, S., Romby, P., Ehresmann, B. and Mattaj, I.W. (1998) The role of exportin-t in selective nuclear export of mature tRNAs. EMBO J., 17, 7430-7441. 

Stade, K., Ford, C.S., Guthrie, C. and Weis, K. (1997) Exportin 1 (Crmlp) is an essential nuclear export factor. Cell, 90,... 

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