17. Which one is incorrect?
(A)Generally, proteolytic maturation occurs in secretory or transport vesicles carrying proteins from the trans-Golgi network to the cell surface.
(B)Generally, ER signal sequences are located at the C-terminus and are cleaved from the protein in the rough ER lumen.
(C)Secretory proteins, enzymes destined for the ER, Golgi complex, and lysosomes, and integral plasma-membrane proteins are synthesized on ribosomes bound to the rough ER. Synthesis of this class of proteins is initiated on membrane-unattached ribosomes.
(D)In both nuclear export and import, the protein to be transported contains a specific amino acid sequence that functions as a nuclear-export signal (NES) or a nuclear-localization signal (NLS). Nucleus-restricted proteins contain a NLS but not a NES, whereas proteins that shuttle between the nucleus and cytosol contain both signals.