Disappearance of a major cell‐type specific surface glycoprotein antigen (SF) after transformation of fibroblasts by rous sarcoma virus

Normal chick fibroblasts are known to contain a tissue‐specific surface component, a major glycoprotein (SF) antigen that is also present in chicken serum. This antigen was greatly reduced in amount or absent in fibroblasts transformed by five different Rous sarcoma virus strains. Fibroblasts infected with virus mutants temperature sensitive for transformation recovered the SF antigen when maintained at the non‐permissive temperature. Productive infection with a non‐transforming avian type‐C virus did not alter the level of SF antigen characteristic of normal fibroblasts. Polyacrylamide gel electrophoresis of total cell extracts indicated that proteins with apparent mol. wt. of 145,000 and mol. wt. 210,000 were greatly decreased following transformation of the fibroblasts. That the ability to synthetize the 145,000 mol. wt. polypeptide was lost upon transformation was implied by pulse labelling experiments, in which normal fibroblasts incorporate [35S] methionine into the above polypeptide whereas transformed cells lose this ability. This polypeptide, unique in its presence in normal but not in transformed cells, appears to have an exceptionally high rate of turnover. Indirect evidence suggests that the 145,000 and 210,000 polypeptides are molecular counterparts of the SF antigen. The transformation‐associated change in the quantity of the SF molecule supports our proposal that tissue‐specific surface glycoproteins, such as the SF antigen, express the stage of differentiation at the membrane of normal cells and may be involved in intercellular control of growth and movement.