Tandem integration of avian retroviruses in double-infected cells

Chicken embryo fibroblasts were chronically infected by both RAV-1 and SR-E, and established SR-E-transformed quail cells were superinfected with RAV-1. About 75 and 50% of double-infected and superinfected cells, respectively, produced both parental viruses. The DNA purified from these cells contained infectious provirus of both parents and no detectable recombinant provirus. In assays using agar overlay, about 5% of the transformed foci that were induced by the DNA of double-infected, but not superinfected, cells were found to contain the progeny of both parents. This observation suggests that in double infections with avian retroviruses, DNA of both parent viruses may integrate into the host genome either in tandem or in close proximity.