Retroviral capture of c-erbB proto-oncogene sequences: rapid evolution of distinct viral genomes carrying mutant v-erbB genes with different transforming capacities.
The evolution of oncogene-transducing retroviruses was followed by studying the genomes of five new, erbB carrying retroviruses. These viruses, isolated from cells of one chicken infected with Rous Associated virus 1 (RAV-1), had captured c-erbB sequences as a consequence of RAV-1 integration into the host genome. Their genome structures were distinct; however, their v-erbB genes had sustained identical 5' and 3' deletions and the v-erbB-env junctions were identical at the nucleotide level. The results therefore strongly suggest that all five viruses originate from the same capture event. Sequence analyses of the v-erbB genes from three of these viruses revealed that one of them had undergone no further mutation and lacked detectable capacity to transform cells, therefore probably representing an 'early' form of transducing virus. The two other v-erbB genes contained distinct mutations and differed in their potential to induce fibroblast- and erythroblast transformation; they therefore probably represent later derivatives of the virus that captured the erbB oncogene. The data suggest that the initial retrovirus rapidly underwent many alterations after capture of c-erbB sequences, already in the RAV-1 infected bird as well as during subsequent in vitro isolation procedures. The changes involve both major rearrangements of the genome as well as point mutations that activated the erbB oncogene.