Final answer:
Protein targeting to the nucleus involves importin, NLS protein, Ran, GEF, and GAP. Importin recognizes and binds to the NLS present in the protein, while Ran acts as a molecular switch for the release of the protein. GEF promotes the exchange of GDP for GTP on Ran, and GAP hydrolyzes the bound GTP to return Ran to its inactive state.
Step-by-step explanation:
Protein targeting to the nucleus is a process by which proteins are transported from the cytoplasm into the nucleus. One of the key players in this process is importin, which is a nuclear transport receptor that recognizes and binds to the nuclear localization signal (NLS) present in the protein.
The NLS is a short amino acid sequence, such as -pro-pro-lys-lys-arg-lys-val-, that acts as a tag to target the protein to the nucleus. Once the importin-protein complex enters the nucleus, the small GTPase protein Ran plays a critical role in the release of the protein by functioning as a molecular switch. The Ran-GTP complex interacts with importin, causing a conformational change that releases the protein from importin and allows it to carry out its function within the nucleus.
The Ran-GTP complex is formed by the action of a guanine nucleotide exchange factor (GEF), which promotes the exchange of GDP for GTP on Ran, and a GTPase-activating protein (GAP), which hydrolyzes the bound GTP to GDP returning Ran to its inactive state.