Mutant avian erythroblastosis virus with restricted target cell specificity

Avian erythroblastosis virus (AEV) induces a fatal erythroblastosis within 2 weeks of intravenous injection in chicks in virtually 100% of cases. In chicks injected intramuscularly, sarcomas frequently develop at the site of injection before the animals die from erythroblastosis 1 . In vitro , AEV transforms both erythroblasts, derived from bone marrow cultures, and fibroblasts. These effects have been shown to be a general property of AEV and not of separate leukaemia- and sarcoma-inducing forms of the virus 2 . AEV is defective for replication and can be propagated only in the presence of helper virus. Its transformation specificity is independent of the helper virus used 2 . It is not clear whether AEV has two different genes controlling transformation of the two types of target cell or whether it has only one gene coding for both. To investigate this question, we looked for mutants of AEV unable to transform one of the two types of target cell. We now describe such a mutant, which is defective for erythroblast transformation but which can still transform fibroblasts.