Simian virus 40 (SV40) is a small, double-stranded DNA virus belonging to the Polyomavirus family. It was first discovered in the early 1960s in cultures of rhesus monkey kidney cells and was later found to be a contaminant in some polio vaccines. SV40 is a non-enveloped virus with an icosahedral capsid and has a genome of approximately 5,200 base pairs.
The SV40 genome contains the following key genes:
- Early region: This region encodes the large T-antigen (LT) and small T-antigen (ST), which are produced from alternatively spliced transcripts. The T-antigens play essential roles in the regulation of the viral life cycle, including viral DNA replication, transcription, and host cell transformation.
- Large T-antigen: The LT is a multifunctional protein that is essential for initiating viral DNA replication and regulating viral transcription. It also has the ability to bind to and inactivate tumor suppressor proteins, such as p53 and Rb, leading to cell cycle dysregulation and cellular transformation.
- Small T-antigen: The ST is involved in the regulation of cellular signaling pathways and contributes to the transformation of host cells, although its precise role in the viral life cycle is not fully understood.
- Late region: The late region of the SV40 genome encodes the structural proteins VP1, VP2, and VP3, which assemble to form the viral capsid.
- VP1: This is the major capsid protein and makes up the outer shell of the icosahedral capsid. VP1 is responsible for receptor binding and is essential for viral entry into the host cell.
- VP2 and VP3: These are minor capsid proteins that associate with the viral genome and contribute to the stabilization of the capsid structure.
- Regulatory elements: The SV40 genome also contains regulatory elements, such as the origin of replication (ori) and promoters that control the expression of early and late genes.
While SV40 is not known to cause disease in humans, it has been widely used as a model system for studying various aspects of molecular and cellular biology, including DNA replication, transcription, and cellular transformation. Additionally, SV40 has served as a tool for gene delivery and the development of gene therapies, as well as an expression vector for recombinant protein production.
