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7 Genetics of Retroviruses

Maxine Linial, Donald Blair


In the nine years since the first edition of this book (Tooze 1973), many advances have been made in our understanding of the structure and function of the genomes of the RNA tumor viruses. Much of the progress has been aided by the isolation and subsequent characterization of viral mutants, both conditional and nonconditional. When the earlier edition was written, attempts were being made to classify viral mutants into groups on the basis of their biological behavior in temperature-shift experiments as well as their effect on replication and/or transformation. The major gene products, which have been subsequently identified, mapped, and characterized, were unknown. And yet many of the mutants isolated prior to 1973 are still being used to obtain a more detailed understanding of the viral genome.

This chapter includes descriptions of the early results with mutants (mainly of avian Rous sarcoma virus [RSV]) in light of what is currently known. The characteristics of spontaneous and induced mutants and variants of nondefective (nd) and defective RNA tumor viruses are presented, as well as the usefulness of such mutants in the elucidation of our current understanding of the viral genome and its functions. Finally, viral phenotypic and genotypic interactions are described, including the high-frequency recombination unique to the retroviruses.

Most of the information on the coding capacity of the genomes of RNA tumor viruses, as well as detailed analysis of the various gene products, has come from the study of the nondefective transforming avian sarcoma virus, RSV. RSV has...

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