Final answer:
With Ran-GAP in the nucleus and Ran-GEF in the cytosol, nuclear protein import would be stalled, whereas export would continue normally due to the directionality provided by Ran-GTP gradients.
Step-by-step explanation:
If all Ran-GAP activity is limited to the nucleus and all Ran-GEF activity is limited to the cytosol, protein import into the nucleus would be stalled, but export would be unaffected. This is because Ran-GTP is generated in the nucleus through the action of Ran-GEF, providing directionality for importins to release their cargo. Exportins, on the other hand, require Ran-GTP to interact with their cargo, and since Ran-GAP is present in the nucleus and not the cytosol, the hydrolysis of Ran-GTP to Ran-GDP, which is necessary for cargo release on the cytosolic side, would proceed normally.
If all Ran-GAP activity is confined to the nucleus, and all Ran-GEF activity is confined to the cytosol, the process of protein import into the nucleus would indeed be hindered, while export would remain unaffected. The generation of Ran-GTP, critical for the directionality of importin release, occurs in the nucleus through the action of Ran-GEF. Importins, responsible for importing proteins into the nucleus, rely on the presence of Ran-GTP. Since Ran-GAP is localized in the nucleus, the hydrolysis of Ran-GTP to Ran-GDP, necessary for cargo release on the cytosolic side, would proceed normally.
Conversely, for protein export from the nucleus, exportins interact with their cargo in the presence of Ran-GTP. The hydrolysis of Ran-GTP to Ran-GDP, crucial for cargo release on the cytosolic side, remains unaffected since Ran-GAP is not present in the cytosol. This asymmetry in Ran-GTP/GDP regulation contributes to the directionality of nucleocytoplasmic transport, emphasizing the importance of spatially regulated Ran-GAP and Ran-GEF activities.