Detection and enumeration of transformation-defective strains of avian sarcoma virus with molecular hybridization.

Serial propagation of avian sarcoma viruses generates deletions in the viral gene responsible for cellular transformation (src). We have devised an assay for these deletion mutants which utilizes molecular hybridization and exploits the availability of DNA (cDNA_sarc) complementary to the nucleotide sequences affected by the deletion in src. Our procedure is also applicable to deletions in other viral genes and offers several advantages over conventional bioassays for the deletion mutants; moreover, it can be used to detect deletions in virus-specific intracellular nucleic acids. In order to illustrate the utility of the assay, we demonstrate that all 20 copies of the proviral DNA for avian sarcoma viruses in XC cells contain src, and we show that single avian cells can contain functioning proviruses for both avian sarcoma virus and a congenic deletion mutant. It should now be possible to use molecular hybridization to study the mechanism by which deletions in src are generated.