The importin-beta family member Crm1 p bridges the interaction between Rev and the nuclear pore complex during nuclear export

Abstract

Background: The human immunodeficiency virus (HIV-1) uses the viral protein Rev to regulate gene expression by promoting the export of unspliced and partially spliced viral transcripts. Rev has been shown to function in a variety of organisms, including Saccharomyces cerevisiae. The export activity of Rev depends on a nuclear export signal (NES), which is believed to interact either directly or indirectly with the nuclear pore complex to carry out its export function. Crm1 p is a member of the importin-beta protein family, other members of which are known to be directly involved in nuclear import. Crm1 p has recently been shown to contribute to nuclear export in vertebrate systems. Here, we have studied this mechanism of nuclear to cytoplasmic transport. Results: Viable mis-sense mutations in the CRM1 gene substantially reduced or eliminated the biological activity of Rev in S, cerevisiae, providing strong evidence that Crm1p also contributes to transport of Roy NES-containing proteins and ribonucleoproteins in this organism. Crm1 p interacted with FG-repeat-containing nuclear pore proteins as well as Rev, and we have demonstrated that the previously described two-hybrid interaction between Rev and the yeast nuclear pore protein Rip1 p is dependent on wild-type Crm1 p. Conclusions: We conclude that Crm1p interacts with the Rev NES and nuclear pore proteins during delivery of cargo to the nuclear pore complex. Our findings also agree well with current experiments on Crm1p orthologs in Schizosaccharomyces pombe and in vertebrate systems.