Figure 3.

Two distinct assembly mechanisms of the NPC. (A) Postmitotic NPC assembly proceeds by a radial dilation of small membrane openings 24. The initial prepore contains dense material in the center of the membrane hole as well as the nuclear ring. It dilates radially and obtains active transport competence during the inner ring and the cytoplasmic ring complex assembly. The central channel continues to maturate even after the membrane dilation stops, and the NPC gradually obtains permeability barrier function against small proteins. Molecular players involved in individual steps of the assembly are indicated below. Possible molecular requirements are shown in gray. ONM, outer nuclear membrane; INM, inner nuclear membrane. (B) Interphase NPC assembly proceeds by an inside‐out extrusion of the nuclear membrane 27 . The intermediate is a dome‐shaped evagination of the INM, that contains the nuclear ring structure underneath the INM from the beginning and grows in size vertically and laterally until it fuses with the flat ONM. Possible molecular players in individual steps of the assembly are shown as in (A).