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We studied the cellular requirements for the translocation of CRM1 (exportin 1) between the nucleus and the cytoplasm. CRM1 import requires neither ATP, Ran, Ran-dependent GTP hydrolysis, nor a particular temperature. CRM1 and importin beta compete with each other during their import. Thus, CRM1 is able to enter the nucleus in a manner similar to importinbeta. In contrast, the in vivo export of CRM1 involves ATP-consuming step(s).

The human immunodeficiency virus type 1 (HIV-1) regulatory protein, Rev, mediates the nuclear export of unspliced gag and singly spliced env mRNAs by bridging viral RNA and the export receptor, CRM1. Recently, rat CRM1 was found to be less efficient than human CRM1 in supporting Rev function in rats. In this study, to understand the role of CRM1 in HIV propagation, the mechanism underlying the function of human and rat CRM1 in HIV-1 replication was investigated in rat cells. The production of viral particles, represented by the p24 Gag protein, was greatly enhanced by hCRM1 expression in rat cells; however, this effect was not simply because of the enhanced export of gag mRNA. The translation initiation rate of gag mRNA was not increased, nor was the Gag protein stabilized in the presence of hCRM1. However, the processing of the p55 Gag precursor and the release of viral particles were facilitated. These results indicated that hCRM1 exports gag mRNA to the cytoplasm, not only more efficiently than rCRM1 but also correctly, leading to efficient processing of Gag proteins and particle formation. [ABSTRACT FROM AUTHOR]

We studied the cellular requirements for the translocation of CRM1 (exportin 1) between the nucleus and the cytoplasm. CRM1 import requires neither ATP, Ran, Ran-dependent GTP hydrolysis, nor a particular temperature. CRM1 and importin β compete with each other during their import. Thus, CRM1 is able to enter the nucleus in a manner similar to importinβ. In contrast, the in vivo export of CRM1 involves ATP-consuming step(s). [ABSTRACT FROM PUBLISHER]