ABSTRACT
Viruses of the Papovaviridae include papilloma and polyoma viruses, and simian vacuolating virus (SV40). SV40-like viruses have been isolated from the brains of patients with progressive multifocal leukoencephalopathy and then from urine of immunosupressed individuals. Papilloma virions are structurally similar to those of polyoma but are slightly larger. Papilloma viruses are easily recovered from extracts of warts and can be seen by direct electron microscopy (EM) of wart tissue. However, these viruses do not replicate in tissue culture. Capsomeres of the virus are easily seen by negative staining EM. These viruses produce papillomas or benign warts in mammals, including man. Polyoma virions are naked icosahedrons about 45 nm in diameter composed of 72 capsomeres in a skew arrangement with T = 7 symmetry. Viral DNA replication occurs in supercoiled intermediates with several distinct proteins expressed from the same DNA segment.
