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13 Genetics of RNA Tumour Viruses


The genetic analysis of RNA tumour viruses is in its infancy and questions such as how many genes these viruses have and how the functions they specify bring about virus replication and cell transformation have yet to be answered. Over the past few years, however, a steadily increasing number of reports of the isolation and characterization of mutant strains of RNA tumour viruses have appeared, and preliminary analyses of recombination between these viruses have been made. In short, the genetic analysis of RNA tumour viruses has begun.

The classical approach to the genetic analysis of the small genomes of viruses is to isolate mutants which can be characterized both physiologically and genetically. Such mutants fall into two classes: (1) conditional mutants, which are particularly suited to physiological experiments because the gene containing the mutation continues to function in permissive environments but fails to function in nonpermissive environments—this means that the gene function can be identified and the time at which it acts during infection determined; (2) nonconditional mutants, which lack this advantage. The gene bearing the nonconditional lesion is inactive under all conditions. But such mutants have one advantage—they are generally more stable than conditional mutants and are therefore suited for the fine analysis of the genome.

At present we know a great deal more about the genetics of the avian RNA tumour viruses than the mammalian RNA tumour viruses (see reviews by Vogt, 1972 and Vogt et al., 1972), not least because the relationship between the avian...

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