Component of the nuclear pore complex (NPC), a complex required for the trafficking across the nuclear envelope. Functions as a scaffolding element in the nuclear phase of the NPC. Plays a role in chromosomal organization and gene expression regulation; stimulates transcription by promoting the formation of an open chromatin environment. Binds chromatin to nucleoporin-associated regions (NARs) that define transcriptionally active regions of the genome. Associates with extended chromosomal regions that alternate between domains of high density binding with those of low occupancy. Preferentially binds to NARs of the male X chromosome. In males, together with Nup153, required for the localization of the male-specific lethal (MSL) histone acetyltransferase complex to the X chromosome and therefore for the transcription of dosage compensation genes. In males, restrains dosage-compensated expression at the level of nascent transcription probably by interacting with the MSL complex and by modulating RNA Polymerase II phosphorylation status and activity. During mitosis forms a gel-like spindle matrix complex together with Skeletor (Skel), Chro, east, and Asator embedding the microtubule spindle apparatus. During interphase localizes Mad1 to the nuclear pore complex and thereby might act as a scaffold to assemble the Mad1-C-Mad2 complex, a heterotetramer that catalyzes the structural conversion of open-Mad2 (O-Mad2) into closed-Mad2 (C-Mad2) which is essential for spindle-assembly checkpoint (SAC). During the metaphase-anaphase transition and before chromosome congression, is phosphorylated by Msp-1; this modification releases Mad1 from the nuclear pore complex and thereby promotes assembly of SAC ensuring a timely and effective recruitment of spindle checkpoint proteins like Mad1, Mad2 and Mps1 to unattached kinetochores (KT). In testes, has a role in stem cell asymmetric division and maintenance via regulation of mitotic spindle assembly checkpoint (SAC) complex