Complex sentence: Once the cargo protein is bound, importin-β interacts with the NPC, and the complex enters the nucleus from the cytoplasm, where it interacts with the Ras-family GTPase, Ran-GTP.
Split into simpler sentences: Once the cargo protein is bound, importin-β interacts with the NPC, and the complex diffuses into the nucleus from the cytoplasm. Once inside the nucleus, the complex interacts with the Ras-family GTPase, Ran-GTP.