Molecular adapter that acts as a bridge between a variety of multiprotein complexes, and which is involved in embryonic development, immunity, myogenesis and brain development (By similarity). Plays a key role in nuclear protein degradation by promoting import of proteasomes into the nucleus: directly binds to fully assembled 20S proteasomes at one end and to nuclear import receptor IPO9 at the other end, bridging them together and mediating the import of pre-assembled proteasome complexes through the nuclear pore (By similarity). Involved in innate immunity by regulating the production of interleukin-6 (IL6) downstream of Toll-like receptor (TLR): acts by bridging the NF-kappa-B inhibitor NFKBIZ and the SWI/SNF complex, leading to promote induction of IL6 (By similarity). Also involved in adaptive immunity by promoting B-cell activation (By similarity). Involved in brain development: required for the survival and proliferation of cerebral cortical progenitor cells (By similarity). Involved in myogenesis: required for skeletal muscle formation and skeletal development, possibly by regulating expression of muscle differentiation factors (PubMed:25686036, PubMed:28327665). Homodimer. Interacts with IPO9; the interaction is direct. Associates with 20S and 26S proteasomes (By similarity). Interacts with SMARCD1; promoting SWI/SNF complex recruitment. Interacts with NFKBIZ (By similarity). Interacts with YWHAB (By similarity). Present mainly in the nuclear fraction, and at much lower level in the cytoplasmic and membrane fractions. Widely expressed (PubMed:22537061). Most abundant in the lung, followed by the skeletal muscle, heart, liver, fat, thymus, lymph node, small intestine, kidney and spleen (PubMed:22537061). In skeletal muscle, expressed at higher level in fast extensor digitorum longus (EDL) and longissimus lumborum (LL) muscles than in slow soleus (SOL) muscles (PubMed:25686036). Belongs to the akirin family.