Control of mRNA Export and Translation Termination by Inositol Hexakisphosphate Requires Specific Interaction with Gle1

The unidirectional translocation of messenger RNA (mRNA) through the aqueous channel of the nuclear pore complex (NPC) is mediated by interactions between soluble mRNA export factors and distinct binding sites on the NPC. At the cytoplasmic side of the NPC, the conserved mRNA export factors Gle1 and inositol hexakisphosphate (IP₆) play an essential role in mRNA export by activating the ATPase activity of the DEAD-box protein Dbp5, promoting localized messenger ribonucleoprotein complex remodeling, and ensuring the directionality of the export process. In addition, Dbp5, Gle1, and IP₆ are also required for proper translation termination. However, the specificity of the IP₆-Gle1 interaction in vivo is unknown. Here, we characterize the biochemical interaction between Gle1 and IP₆ and the relationship to Dbp5 binding and stimulation. We identify Gle1 residues required for IP₆ binding and show that these residues are needed for IP₆-dependent Dbp5 stimulation in vitro. Furthermore, we demonstrate that Gle1 is the primary target of IP₆ for both mRNA export and translation termination in vivo. In Saccharomyces cerevisiae cells, the IP₆-binding mutants recapitulate all of the mRNA export and translation termination defects found in mutants depleted of IP₆. We conclude that Gle1 specifically binds IP₆ and that this interaction is required for the full potentiation of Dbp5 ATPase activity during both mRNA export and translation termination.