A self-inhibitory interaction within Nup155 and membrane binding are required for nuclear pore complex formation

Nuclear pore complexes (NPCs) are gateways through the nuclear envelope. How they form into a structure containing three rings and integrate into the nuclear envelope remains a challenging paradigm for coordinated assembly of macro-complexes. In vertebrates, the cytoplasmic and nucleoplasmic rings of NPCs are mostly formed by multiple copies of the Nup107-Nup160 complex, whereas the central, or inner ring is composed of Nup53, Nup93, Nup155 and the two paralogues Nup188 and Nup205. Inner ring assembly is only partially understood. Using in vitro nuclear assembly reactions, we show that direct pore membrane binding of Nup155 is crucial for NPC formation. Replacing full-length Nup155 with its N-terminal beta-propeller allows assembly of the outer ring components to the NPC backbone that also contains Nup53. However, further assembly, especially recruitment of the Nup93 and Nup62 complexes, is blocked. Self-interaction between the N- and C-terminal domains of Nup155 has an auto-inhibitory function that prevents interaction between the N-terminus of Nup155 and the C-terminal region of Nup53. Nup93 can overcome this block by binding to Nup53, thereby promoting formation of the inner ring and the NPC.