[Study of the population composition of the Rous sarcoma virus Carr-Zilber strain]

The population composition of the Carr-Zilber high titer (HT) strain of Rous sarcoma virus (C-Z-RSV) was analysed with regard to 2 features: the capacity to impart oncogenicity for syngeneic recipients to infected but untransformed cultures of mouse embryo tissue (MET), and oncogenicity for mice. With regard to these features the C-Z-RSV (HT) strain was found to be heterogenic and to consist of particles of at least two types: non-oncogenic for mice and incapable of causing early malignization of MET, and oncogenic for mice and causing early malignization.