Nuclear mRNA export requires coordinated FG‐Nup binding and DEAD‐box protein‐mediated remodeling events

Abstract

Nucleocytoplasmic transport of proteins and nucleic acids is essential for proper gene expression. Using the Saccharomyces cerevisiae model, we discovered key events for directional export of messenger (m) RNA. Distinct steps were pinpointed at nuclear, central and cytoplasmic nuclear pore complex (NPC) structures. Nearly half of the ∼30 NPC proteins harbor Phe‐Gly (FG) repeat domains that potentially serve as binding sites for the shuttling mRNA export receptor Mex67. A large‐scale deletion strategy was employed to generate mutants lacking discrete combinations of FG‐domains, and specific subsets of FG domains were required for mRNA export. The FG mutants also revealed multiple functionally independent translocation routes through NPCs. mRNA export required FG domains on the nuclear NPC face (presumably for initial docking at the NPC) and in the NPC central core. At the cytoplasmic NPC face, we found that the RNA‐dependent ATPase activity of the DEAD‐box protein Dbp5 was stimulated by inositol hexakisphosphate‐bound Gle1. The ADP‐bound form of Dbp5 triggered release of the RNA‐binding protein Nab2 from RNA. This novel nucleotide‐dependent switch mechanism remodeled mRNA‐protein complexes for directional translocation. We predict that these FG‐binding and mRNP remodeling steps are coupled for spatial regulation of mRNA export through and subsequent release from the NPC.Supported by grants from the NIGMS.