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A ts T mutant of Schmidt ruppin strain of rous sarcoma virus restricted at 39.5°C for the morphological transformation and the tumorigenicity of chicken embryo fibroblasts

In order to investigate a possible correlation beween in vitro transformation and tumorigenicity in ovo, a new temperature‐sensitive class T mutant of Rous Sarcoma Virus was isolated with a lower (39·5C) restrictive temperature for morphological transformation. This lower restrictive temperature was compatible with the survival of chicken and duck eggs for the tumorigenicity studies. In chicken embryo fibroblasts (CEF) infected by this new mutant, PA 17, and cultured at 39·5C, increase of hexose uptake, plasminogen activator production and anchorageindependent growth were only partially restricted, requiring incubation at 41·5C for a complete shut‐off. Tumorigenicity in chicken and duck eggs inoculated with CEF infected and transformed by PA 17 was restricted at 39·5C, correlating well with the restriction of morpholgical transformation at this temperature. The kinase activity of the transforming protein pp in lysates of PA 17 infected cells cultured at permissive or restrictive temperatures was labile in RIPA buffer, as in the case of some previously examined tsT mutants. In the non‐ionic detergent NP40 buffer, the kinase activity of PA 17 infected cell lysates was better conserved and showed a moderate temperature dependence. These results suggest that, in spite of the correlations between the transformed cell phenotype in vitro and cell tumorigenicity in ovo, it is difficult to establish a quantitative relationship.