Infectious dna recovered from avian tumor‐virus‐producing cells

A single treatment of chick embryo fibroblasts with DNA recovered from chick embryo fibroblasts productively infected and transformed with four different strains of RSV, or productively infected with two different strains of RAV, resulted in virus production and cell transformation (in the case of RSV) two or three passages after treatment (8–25 days). The virus recovered from cultures was phenotypically identical to that produced by the donor cells. No virus production nor cell transformation resulted from treatment of control cultures with DNA digested with DNAse. Infectious RSV‐DNA was recovered from purified donor cell nuclei and was associated with the precipitable fraction of DNA prepared according to the method of Hirt (1967). It also sedimented with cellular DNA in density gradients, and with high molecular weight DNA (2–4 × 10 7 daltons) in sucrose gradients, which suggests that it is associated and may be integrated with chromosomal DNA. In some experiments, DNA fractions of lower molecular weight (down to 6 × 10 6 daltons) were also infectious. DNA from virus‐producing RSV‐transformed cells also gave rise to virus and Rous cells in cultures of fibroblasts from gs ‐ embryos. However, the amount of DNA required for successful infection varied widely between experiments, and no reproducible dose‐effect relationship was observed. The frequency of DNA‐treated cells which produced virus remained low, even when the assay cultures were pretreated with 5‐bromodeoxyuridine.