5 Genetics of SV40 and Polyoma Virus

Abstract

For viruses with genomes of so limited a capacity, SV40 and polyoma virus show a surprising variety of interactions with host cells, ranging from productive infections, when total expression of viral functions occurs, through the poorly understood semipermissive systems, to transformation, when only a subset of viral genes is expressed. Fortunately, there is a great wealth of mutants available for genetic studies. These include host-range mutants of polyoma virus, which are able to replicate only on certain kinds of mouse cells (Benjamin 1970; Goldman and Benjamin 1975; Benjamin and Goldman 1975; Staneloni et al. 1977); mutants that fail to grow at low temperature (Kimura 1973); mutants that fail to adsorb to some types of cells (Basilico and di Mayorca 1974); mutants with defective, substituted, or rearranged genomes (Scott et al. 1976; see also Chapter 2); and the extensively studied mutants whose growth at high temperature is significantly less than at low temperature ( ts mutants; see below). The genetic lesions in many of these mutants have been classified on the basis of complementation tests and have been assigned to physical locations on the viral genome. By studying the behavior of mutants it has been possible to map functional domains on the viral DNA. The aim of all this work has been to relate the expression of various genes to the several effects that the viruses produce in cultured cells. TEMPERATURE-SENSITIVE MUTANTS Temperature-sensitive ( ts ) mutants result from alterations in the base sequence of DNA that, in turn, cause changes in the amino...