What is the role of the nuclear localization sequence in a nuclear protein?
(a) It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore.
(b) It is a hydrophobic sequence that enables the protein to enter the nuclear membranes.
(c) It aids in protein unfolding so that the protein can thread through nuclear pores.
(d) It prevents the protein from diffusing out of the nucleus through nuclear pores.
Choice (a) is correct. The nuclear localization signal typically contains positively charged amino acids, not hydrophobic ones [choice (b)]. Proteins are not unfolded as they enter the nucleus [choice (c)]. Proteins are actively transported in and out of the nucleus and do not diffuse through the nuclear pores [choice (d)].
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