Final answer:
The NLS of SV40 T-antigen refers to the Nuclear Localization Signal which allows the T-antigen to enter the host cell's nucleus and interfere with normal cell cycle control, particularly through binding with the p53 protein, potentially leading to cancerous tumor formation.
Step-by-step explanation:
The NLS of SV40 T-antigen stands for Nuclear Localization Signal of the SV40 Large T-antigen. This sequence is critical for the T-antigen to be transported into the nucleus of the host cell. Once inside the nucleus, the T-antigen plays a vital role in regulating the transcription of genes essential to viral replication and viral particle formation. The Large T-antigen of SV40 is known to bind to the p53 protein, which is a key player in cell cycle regulation and apoptosis. This interaction can lead to the cell's inability to properly regulate the cell cycle, thus potentially resulting in uncontrollable division and the formation of cancerous tumors. The SV40 virus, once a viral contaminant of polio vaccines used in the 1960s, is noted for its ability to cause tumors in mammals, although a definitive link to human cancer remains unproven. Nevertheless, the study of SV40 and its interaction with cellular mechanisms such as those involving p53 has contributed significantly to our understanding of cell biology and oncogenesis.