Printed in Great Britain Activation of protein kinase C modulates the expression of the T3/T cell

15 min) in the surface expression of the T3 antigen and T-lymphocyte antigen receptor (Ti) on HPB-ALL cells, and a concomitant phosphorylation f the T3 3 ' and ~ polypeptides; the 3 ̀chain was more extensively phosphorylated than the chain. No phosphorylation f the T3 e chain and the Ti a and polypeptides was detected. Evidence was obtained that the T3 3 ̀chain is phosphorylated only on serine residues. In T-lymphocytes, antigen recognition and the associated initiation of T-cell activation is mediated by a macromolecular complex comprising the idiotypic antigen receptor (Ti) linked non-covalently to the invariant T3 antigen (Meuer et al., 1983a, b, c; Haskins et al., 1983). Ti is a heterodimer of two disulphide-bonded, glycosylated polypeptides of about 50 000 and 43 000 mol.wt. ( ~ and ~ respectively) (Acuto et al., 1983), whereas T3 com-prises two N-glycosylated polypeptides of about 26 000 and 21 000 mol.wt. (3 ' and 6 respectively) and one non-N-glycosylated polypeptide of abou