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7 Genetics of Polyoma Virus and SV40


The idea that the properties of transformed cells can be influenced by the expression of viral genes stems from the observations that viral DNA can become part of the genetic material of transformed cells and that virus-specific products persist in transformed cells. By isolating mutant viruses with defective functions, it should be possible to associate a particular viral gene product with particular changes which occur on transformation. To this end temperature-sensitive mutants of polyoma virus and recently SV40, and host-range mutants of polyoma virus have been selected.

The isolation of temperature-sensitive mutants of polyoma virus was first reported in 1965 by Fried, but for reasons that are obscure attempts to isolate comparable mutants of SV40 failed for several years. During the past two years, however, several groups have managed to obtain useful SV40 mutants. Not surprisingly, today we know more about the polyoma virus mutants than the SV40 mutants simply because the former have been studied for a considerably longer time. But this state of affairs is changing quite rapidly. SV40 seems to be more convenient to handle in the laboratory than polyoma virus and it can be readily rescued from transformed cells; as a result we know far more about SV40 than polyoma virus, with the exception of the genetics of these viruses, and this exception seems destined to be short lived.

Temperature-sensitive mutants of polyoma virus have been isolated after treating large-plaque polyoma virus with nitrous acid (Fried, 1965a; Vogt, unpublished data; di...

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