Final answer:
The large T antigen is a protein in polyomavirus that aids in viral replication and can transform host cells into cancerous cells by deregulating the cell cycle and binding to p53 protein.
Step-by-step explanation:
The large T antigen in polyomavirus, specifically in SV40, is a multifunctional protein crucial for viral replication and the manipulation of host cellular processes.
This antigen enters the host cell nucleus, where it plays a role in transforming normal cells into cancerous ones. It does this by binding to the p53 protein and interfering with its transcriptional regulation, leading to uncontrolled cell division and potentially the formation of cancerous tumors.
Moreover, the large T antigen ensures that the infected cell progresses to the S phase, which is necessary for both viral DNA replication and host cell DNA co-replication.
This deregulation of the cell cycle by the large T antigen is essential for the virus to usurp the host machinery and propagate the infection, sometimes leading to the development of malignant sarcomas and other tumors.