The small T-antigen (ST) is a protein encoded by some members of the Polyomavirus family, including Simian Virus 40 (SV40), which is a small, double-stranded DNA virus. Small T-antigen is expressed during the early phase of the viral life cycle, along with the large T-antigen (LT).

Although the precise role of small T-antigen in the viral life cycle is not fully understood, it is known to be involved in the regulation of cellular signaling pathways and contributes to the transformation of host cells. Small T-antigen has been shown to interact with cellular proteins, such as protein phosphatase 2A (PP2A), which is a key regulator of cell growth and division. This interaction can lead to the disruption of normal cellular processes and contribute to cellular transformation.

Small T-antigen, along with large T-antigen, has been widely studied for its ability to induce cellular transformation and tumorigenesis in experimental models. While small T-antigen alone is generally insufficient to cause full transformation, it can cooperate with large T-antigen to enhance the transforming potential of the virus.

Studying small T-antigen and its interactions with host cell proteins can provide valuable insights into the molecular mechanisms underlying viral replication, cellular transformation, and cancer development. Additionally, understanding the functions of small T-antigen may aid in the development of new therapeutic strategies targeting viral infections and associated diseases.