Simian virus 40 (SV40) is a polyomavirus that is found in both monkeys and humans. It is a DNA virus that sometimes causes tumors in animals, but most often persists as a latent infection. Here are some key points about SV40:

• Contamination of Polio Vaccines: Polio vaccines used in the late 1950s and early 1960s were contaminated with SV40, which was present in monkey kidney cells used to produce the vaccines.

• Role in Cancer: SV40 is a known oncogenic DNA virus that induces primary brain and bone cancers, malignant mesothelioma, and lymphomas. However, the role of SV40 in human cancers is still a topic of debate and research.

• Tumor Antigens: When SV40 infects its natural host, it initially undergoes a lytic replication cycle. The early viral genes encode the tumor (T) antigens: large T antigen (LT), small t antigen (st), and 17kT antigen.

• Genome: The SV40 genome is a double-stranded circular DNA molecule that contains 5243 base pairs, which can be divided into two regions (early and late) according to the timing of gene expression.

SV40 has been widely studied as a model eukaryotic virus, leading to many early discoveries in eukaryotic DNA replication and transcription. Biotechnology companies seek to utilize modified SV40-based vectors as a viral vector for gene therapy.