The needs of the pore

According to a model that has prevailed since the early 1990s, nuclear import complexes need to dock to the cytoplasmic filaments of the nuclear pore complex (NPC) before they can be translocated to the nucleus. On page 63, Walther et al. overturn this idea, demonstrating that cytoplasmic filaments have no essential function in the nuclear import of bulk cargos. The results also provide new insights on the composition of the filaments.

Using the Xenopus egg extract system, the authors analyzed two cytoplasmically oriented nucleoporins, CAN/Nup214 and RanBP2/Nup358. CAN/Nup214 was previously thought to be a component of the cytoplasmic filaments, but in the new work it appears to be located near the entrance to the translocation channel in the NPC. RanBP2/Nup358, however, is an essential component of the cytoplasmic filaments: depleting this protein causes NPCs...