Directs RNA polymerase II nuclear import. Binds RNA polymerase II in the active center cleft between the two largest subunits in the cytoplasm. Then uses an N-terminal bipartite nuclear localization signal that may be recognized by karyopherin alpha to direct the polymerase II complex nuclear import. In the nucleus, is displaced from polymerase II complex by transcription initiation factors and nucleic acids, enabling its export and recycling. Associates with RNA polymerase II. Part of a complex consisting of RPB1, RBP2, RPB3, RPB4, RPB5, RPB7, SPT5, DST1 and IWR1. Shuttles between the nucleus and cytoplasm. Leads to a K1 killer toxin hypersensitivity and pleiotropic effects on gene expression. Present with 1080 molecules/cell in log phase SD medium. Belongs to the IWR1/SLC7A6OS family. Due to the effects of deletion on gene expression, was originally thought to be a general transcription factor (PubMed:19679657). Further studies clearly suggest that it is involved in nuclear localization of the RNA polymerase II complex (PubMed:21504834). Truncated N-terminus.