The RNA export factor Gle1p is located on the cytoplasmic fibrils of the NPC and physically interacts with the FG-nucleoporin Rip1p, the DEAD-box protein Rat8p/Dbp5p and a new protein Ymr 255p

Abstract

Gle1p is an essential, nuclear pore complex (NPC)-associated RNA export factor. In a screen for high copy suppressors of a GLE1 mutant strain, we identified the FG-nucleoporin Rip1p and the DEAD-box protein Rat8p/Dbp5p, both of which have roles in RNA export; we also found Ymr255p/Gfd1p, a novel inessential protein. All three high copy suppressors interact with the C-terminal domain of Gle1p; immunoelectron microscopy localizations indicate that Gle1p, Rip1p and Rat8p/Dbp5p are present on the NPC cytoplasmic fibrils; Rip1p was also found within the nucleoplasm and on the nuclear baskets. In vivo localizations support the hypothesis that Rip1p contributes to the association of Gle1p with the pore and that Gle1p, in turn, provides a binding site for Rat8p/Dbp5p at the NPC. These data are consistent with the view that Gle1p, Rip1p, Rat8p/Dbp5p and Ymr255p/Gfd1p associate on the cytoplasmic side of the NPC to act in a terminal step of RNA export. We also describe a human functional homologue of Rip1p, called hCG1, which rescues Rip1p function in yeast, consistent with the evolutionary conservation of this NPC-associated protein.