What role do importins play in cellular transport?

Importins play a crucial role in the transport of proteins into the nucleus. They function as carrier proteins that bind to cargo molecules, specifically proteins that contain a nuclear localization signal (NLS). This binding enables the importins to ferry these proteins across the nuclear envelope through nuclear pore complexes.

Once the importin-protein complex enters the nucleus, the importins release their cargo, allowing the proteins to perform their functions within the nuclear environment. The process is tightly regulated and essential for cellular function, as many proteins that exert their activities in the nucleus—such as transcription factors—require importins for their transport from the cytoplasm.

The other options reflect different processes and proteins involved in cellular activities, but they do not pertain to the specific function of importins in nuclear import.