Final answer:
Ran-GTP dissociates from Importin and Exportin due to its intrinsic GTPase activity, which is enhanced by accessory proteins such as RanGAP, leading to the hydrolysis of GTP to GDP and subsequent release of the cargo.
Step-by-step explanation:
The dissociation of Ran-GTP from Importin and Exportin in the cytosol is a critical step in the process of nucleocytoplasmic transport. In this mechanism, the GTP-bound form of Ran (Ran-GTP) provides the directionality needed for the transport of cargo molecules either into or out of the nucleus. Specifically, the attachment of Ran-GTP to Importin or Exportin triggers changes that lead to the release of the cargo. This is followed by the hydrolysis of GTP to GDP by Ran’s intrinsic GTPase activity, which turns Ran into its GDP-bound form (Ran-GDP), causing it to dissociate from the transport receptor. This process is regulated by accessory proteins, like RanGAP (Ran GTPase-activating protein) which enhance the GTPase activity of Ran, and the nucleotide exchange factor RCC1 which facilitates the exchange of GDP for GTP on Ran, ensuring that the cycle can continue.