Linkage of the endogenous avian leukosis virus genome of virus-producing chicken cells to inhibitory cellular DNA sequences.

The endogenous avian leukosis virus genome of uninfected virus-producing(V+) chicken embryo fibroblasts appears to be inefficiently transcribed and is noninfectious in transfection assays of high molecular weight DNA. We previously proposed that the endogenous virus genome was linked to a cis-acting control element which inhibited its transcription and, consequently, interfered with transfection by endogenous viral DNA. We now report that DNA of uninfected V+ cells is infectious at a low level when sheared to the approximate size of the virus genome. These results suggest that the endogenous virus genome of uninfected V+ chicken cells can be converted to an infectious form by separating it from adjacent cellular DNA sequences, as predicted by the cis-acting control element model.