Correct option is C
Explanation:
- Nuclear protein import occurs through nuclear pore complexes (NPCs) and involves importins (import receptors) that transport cargo proteins into the nucleus.
- Once inside the nucleus, RanGTP binds to the importin-cargo complex, triggering cargo release.
- Ran (a small GTPase) exists in two states:
- RanGDP (cytoplasm) – inactive form.
- RanGTP (nucleus) – active form, facilitates nuclear import.
- RanGTP binding to importin causes a conformational change, leading to dissociation of the cargo inside the nucleus.
- This ensures the directionality of nuclear transport.
Thus, Ran is responsible for releasing the cargo from the importing receptor inside the nucleus (option 3).
Additional Information
- Option (1) Ras: Incorrect; Ras is involved in signal transduction (MAPK pathway), not nuclear transport.
- Option (2) RhoA: Incorrect; RhoA regulates cytoskeletal dynamics and cell motility, not nuclear transport.
- Option (4) Rock: Incorrect; ROCK (Rho-associated kinase) controls actin cytoskeleton remodeling, not protein import.
