Purified EGF receptor-kinase interacts specifically with antibodies to Rous sarcoma virus transforming protein

Transformation by several RNA tumour viruses seems to be mediated by virally coded protein kinases which specifically phosphorylate tyrosine. A tyrosine-specific protein kinase also seems to be involved in the mitogenic action of epidermal growth factor (EGF). This EGF-stimulated kinase activity is closely associated with the EGF receptor, with which it copurifies during EGF-affinity chromatography. Because both the virus- and EGF-stimulated tyrosine kinases may be involved in stimulation of cell growth, and because the viral kinases may be antigenically related to normal cell proteins, we examined the interaction of antibodies to viral tyrosine kinases with the affinity-purified EGF receptor-kinase preparation. We report here that the receptor-kinase specifically phosphorylates antibodies directed against the transforming protein kinase pp60src of Rous sarcoma virus. However, none of these antibodies, including those which cross-react with the normal cellular homologue of pp60src (pp60sarc), precipitate the receptor-kinase. These results suggest that the EGF receptor-kinase is related to, but probably not identical with, pp60sarc.     

Inability of Rous sarcoma virus to cause sarcomas in the avian embryo

The injection of Rous sarcoma virus (RSV) into the wing web of newly hatched chicks causes a rapidly growing sarcomatous tumour which is palpable within 1 week of inoculation; and cultures of fibroblasts derived from chick embryos (CEF) and infected with RSV become rapidly transformed. Genetic studies have determined that expression of a single viral gene, designated v-src, is necessary for neoplastic transformation. This gene codes for a 60,000-molecular weight phosphoprotein termed pp60SPC , which possesses a protein kinase activity that phosphorylates polypeptides on tyrosine residues and is constitutively expressed in infected CEF cells. It has been suggested that transformation, and possibly tumorigenesis, may result solely from the consequences of this increase in tyrosine phosphorylations. The pathogenicity of RSV in chick embryos in ovo is less clear. Murphy and Rous suggested that RSV may have caused tumours in "various tissues" of "some embryos", but the subsequent studies of Milford and Duran - Reynals , as well as several other laboratories, failed to find any evidence of intraembryonic tumours in RSV-infected early embryos. The findings of Duran - Reynals , if correct, cannot be explained easily in view of our present understanding of RSV tumorigenicity. Thus, we have re-examined the interaction of RSV with the avian embryo and confirm here that RSV is nontumorigenic and non-teratogenic when microinjected into day 4 chicken embryos. In addition, we found that (1) the virus not only replicates in the embryo, but it also expresses an active src-specific protein kinase and (2) once the cells from the infected limbs are disrupted and placed in culture, they are capable of expressing the transformed phenotype after a 24-h delay.     

Initiation sites of Rous sarcoma virus RNA-directed DNA synthesis in vitro.

Rous sarcoma virus DNA synthesis in disrupted virions is initiated mainly at a site about 200 nucleotides or less from the 5' terminus, but other initiation sites throughtout the RNA seem to be used as well. No AUG triplet occurs within a 5' terminal segment of about 25 nucleotides.