Abstract
A series of recombinant retroviral genomes was generated by cotransformation of NIH 3T3 cells with a mixture of cloned DNAs: a proviral copy of the wild-type Moloney murine leukemia virus, and Moloney-based vectors containing defective copies of the chicken v-src and the murine v-abl oncogenes. Morphologically transformed foci, appearing at low frequencies in these cultures, released high titers of transforming viruses. Analysis of one group of these viruses showed that the genomes were recombinants containing portions of the viral gag gene juxtaposed to the v-src oncogene. Biologically active cloned DNAs of two of these viruses were obtained and mapped in detail. One of these viruses did not cause disease after inoculation into newborn mice, but the other induced rapidly fatal hemangiosarcomas located exclusively in the brain.