Product of the src gene is not phosphorylated in avian sarcoma virus B77 infected but untransformed human cells

Human embryo cells infected with the avian sarcoma virus B77 [Hu(B77)] but untransformed, contain the whole rescuable virus genome integrated in the host cell DNA. The cellular DNA induced the transformation of the infectious B77 virus after transfection of chicken cells. In the Hu(B77) cells the src gene product was expressed as a 58 kD protein which possessed phosphokinase activity but was not phosphorylated in comparison with the src production of B77 transformed rat cells RBI in which p60src is expressed. The addition of vanadate to tissue culture fluid reversibly elicited cell transformation in both control and virus infected human cells, but did not influence phosphorylation of the src gene product. The secretion of phosphoproteins in the investigated cells was different. Whereas transformed rat cells released a 62 kD transformation related phosphoprotein, the human cells did not. In tissue culture fluid from Hu(B77) cells an elevated amount of a 22 kD phosphoprotein was found in comparison with control cells. The implications of these findings are discussed with respect to the role of the v-src gene product in malignant cell transformation.