Essential component of the nuclear pore complex (NPC). The repeat-containing domain may be involved in anchoring components of the pore complex to the pore membrane. When overexpressed in cells induces the formation of cytoplasmic annulate lamellae (AL). Stably associated with the NPC throughout interphase and the endoplasmic reticulum during metaphase. Contains F-X-F-G repeats. Proteolytically cleaved by caspase-3 during apoptosis. Belongs to the POM121 family.