Partial characterization and proposed mode of action of inhibitory HeLa cell surface polypeptides

Polypeptides removed from the HeLa cell surface by mild pronase treatment rapidly inhibit protein synthesis when added to HeLa cells or cell-free translation systems derived from HeLa cells. The inhibitory activity is heat stable. Protein and carbohydrate components of these polypeptides are required for inhibition of protein synthesis in vivo and in vitro. Two peaks of activity can be recovered from polyacrylamide gels, corresponding to polypeptides with molecular weights of approximately 29 000 and 41 000. Inhibition of protein synthesis in cell-free translation systems appears to be primarily an effect on elongation of polypeptide chains, whereas in the intact cell the primary target may be polypeptide chain initiation.