CD19 OF B-CELLS AS A SURROGATE KINASE INSERT REGION TO BIND PHOSPHATIDYLINOSITOL 3-KINASE

Antigen receptors on B and T lymphocytes transduce signals by activati ng nonreceptor protein tyrosine kinases (PTKs). A family of receptor P TKs contains kinase insert regions with the sequence tyrosine-X-X-meth ionine (where X is any amino acid) that when phosphorylated mediate th e binding and activation of phosphatidylinositol 3-kinase (PI 3-kinase ). The CD19 membrane protein of B cells enhances activation through me mbrane immunoglobulin M (mIgM) and was found to contain a functional a nalog of the kinase insert region. Ligation of mIgM induced phosphoryl ation of CD19 and association with PI 3-kinase. Thus, CD19 serves as a surrogate kinase insert region for mIgM by providing the means for PI 3-kinase activation by nonreceptor PTKs.