importinok

Importinok is a hypothetical nuclear transport receptor used in theoretical discussions of nucleocytoplasmic trafficking and in teaching materials to illustrate import mechanisms. It is described as a member of the karyopherin family and is typically portrayed as a soluble, HEAT-repeat–containing protein that recognizes cargo carrying a nuclear localization signal.

It binds cargo in the cytoplasm, travels through the nuclear pore complex, and releases the cargo in the nucleus in response to the Ran GTPase gradient. In the nucleus, RanGTP promotes dissociation of the cargo–importinok complex, after which importinok returns to the cytoplasm bound to RanGDP.

It is often depicted as functioning alongside adaptor proteins that increase specificity for certain cargoes, although in many educational models importinok operates as a general transport receptor. Because importinok is not associated with a confirmed protein or gene in current biology, its description serves as a simplified teaching aid and a placeholder for discussing the principles of nuclear import, nuclear pore transport, and Ran-driven recycling.

In this way, importinok helps illustrate core concepts of nucleocytoplasmic transport without tying them to a specific, experimentally verified protein.