Structural characterization of the TAP molecule: A phosphatidylinositol-linked glycoprotein distinct from the T cell receptor/T3 complex and Thy-1

Here we characterize the T-cell-activating protein (TAP), an Ly-6 gene product involved in T cell activation, as a glycoprotein with a molecular weight of 10-12 kd under nonreducing conditions and 15-18 kd under reducing ones. Two of the three bands that are precipitated from metabolically labeled cells are expressed on the cell surface and can be recovered from the supernatants of cells treated with a phosphatidylinositol-specific phospholipase C. Thus TAP appears to be attached to the cell membrane via this lipid. Precisely the same anchorage is observed for the activating Thy-1 molecule, and is therefore of particular interest as a potentially novel linkage involved in membrane signal transduction.