Final answer:
Newly synthesized proteins enter the nucleus by attaching to a nuclear transport receptor via a nuclear localization signal, followed by active transport through the nuclear pore complex with the help of ATP hydrolysis.
Step-by-step explanation:
A newly synthesized protein enters the nucleus through a multistep process that requires a nuclear localization signal, which is usually a sequence of amino acids rich in positively charged residues such as lysine and proline. This signal is recognized by a nuclear transport receptor in the cytoplasm. Once the protein-receptor complex approaches the nuclear pore, it interacts with the pore's fibrils, prompting the pore to open. The protein is then transported across the nuclear envelope through an energy-dependent process, involving ATP hydrolysis, into the nucleus where it can perform its function.