Mediates the nuclear export of proteins (cargos). In the nucleus binds cooperatively to its cargo and to the GTPase Ran in its active GTP-bound form. Docking of this trimeric complex to the nuclear pore complex (NPC) is mediated through binding to nucleoporins. Upon transit of a nuclear export complex into the cytoplasm, disassembling of the complex and hydrolysis of Ran-GTP to Ran-GDP cause release of the cargo from the export receptor. Xpo4 then return to the nuclear compartment and mediate another round of transport. The directionality of nuclear export is thought to be conferred by an asymmetric distribution of the GTP- and GDP-bound forms of Ran between the cytoplasm and nucleus. Interacts with Ran and cargo proteins in a GTP-dependent manner. Shuttles between the nucleus and the cytoplasm. Belongs to the exportin family.