Final answer:
Proteins require a nuclear localization signal (NLS) to transport between the nucleus and the cytosol. This signal allows binding to a nuclear transport receptor protein in the cytosol.
Step-by-step explanation:
Active transport processes, such as vesicle transport and motor proteins, also play a role in protein transport. To transport between the nucleus and the cytosol, proteins require a nuclear localization signal (NLS), which enables binding to a nuclear transport receptor protein in the cytosol. This NLS contains positively charged amino acids (lysine, proline) that bind to the negatively charged domain of the receptor.
The transport of proteins also relies on active transport processes that require ATP, such as vesicle transport and motor proteins that move cargo along microtubule tracks.