This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure and function of protein, Subject name: Biochemistry
[{'content': 'What constitutes the driving force for transpo of proteins into and out of the nucleus? \nSelect and explain. \nA. ATP hydrolysis within the cytosol, B. ATP hydrolysis within the nucleus, C. GTP hydrolysis within the cytosol, D. GTP hydrolysis within the nucleus', 'role': 'user'}, {'content': 'Answer: C \nExplanation: No ATP is involved at any point in nuclear transpo. The driving force for the transpo comes indirectly from a gradient created by GTP hydrolysis. The key controlling factor is the allosteric GTPase, Ran. Ran is only able to hydrolyze GTP to GDP in the cytosol because this process must be activated by a GTPase-activating protein (GAP) that is only present in the cytosol. Reference: Harper; 30th edition', 'role': 'assistant'}]