The SV40 large T antigen Nuclear Localization Signal (NLS) is a specific amino acid sequence within the SV40 large T antigen protein that directs its transport into the cell nucleus. This NLS, located at residues 47-55 (PKKKRKV), is crucial for the protein's function in viral replication and cellular transformation. The NLS acts as a signal that is recognized by importin proteins, which then facilitate the protein's movement through the nuclear pore and into the nucleus.