The Genome of Simian Virus 40

The essential feature of a virus is its nucleic acid genome, a cluster of genes that brings new information into the cell it infects. Depending on the circumstances of infection, expression of viral genes can lead to multiplication of the virus, and perhaps cell damage or to a stable virus-host cell relationship, in which the cell often acquires new properties. These characteristics of viruses, combining the simplicity of the genomic structure and easy manipulation with important cellular effects, accounts for their great usefulness in studying gene action and regulation in complex cells. Among the simplest tumor viruses are the small DNA-containing papo-vaviruses, including simian virus 40 (SV40), the murine polyoma virus, and the human papovaviruses BK and JC. These viruses exhibit similar physical and biological properties, and in some instances partial homology of DNA sequences. Therefore, although this chapter concentrates on SV40, the general features of genomic organization and function are likely to apply to all the small papo-vaviruses. SV40 occurs as an inapparent natural infection of certain species of Asiatic macaques and was discovered in rhesus monkey cell cultures as a vacuolating agent for African green monkey cells. The purpose of this chapter is to examine, in detail, some of the molecular events just outlined and to relate them to the structure and genetic organization of the SV40 genome. The primary focus will be on the SV40 genome itself, its structure as a DNA molecule and small chromosome, its genetic content, its replication and transcription, and its interaction with cellular chromosomes.