A family of proteins involved in NUCLEOCYTOPLASMIC TRANSPORT. Karyopherins are heteromeric molecules composed two major types of components, ALPHA KARYOPHERINS and BETA KARYOPHERINS, that function together to transport molecules through the NUCLEAR PORE COMPLEX. Several other proteins such as RAN GTP BINDING PROTEIN and CELLULAR APOPTOSIS SUSCEPTIBILITY PROTEIN bind to karyopherins and participate in the transport process.