ASSEMBLY OF THE T-CELL ANTIGEN RECEPTOR - PARTICIPATION OF THE CD3-OMEGA CHAIN

The human TCR is composed of the Tialphabeta heterodimer in associatio n with the CD3 chains CD3gammadeltaepsilonzeta2. Another chain, referr ed to as CD3omega, has recently been described in T cells. CD3omega is an intracellular protein transiently associated with the CD3 complex during the assembly of the TCR in the endoplasmic reticulum (ER) and i t is not expressed on the cell surface. The function of CD3omega is un known but it has been suggested that it plays an important role in the assembly of the TCR. We have studied the possible function of CD3omeg a in the human leukemic T-cell line Jurkat and different variants of t his cell line. Cells were metabolically labeled, subjected to lysis, i mmunoprecipitated, and analyzed by SDS-PAGE. The results indicate that : 1) CD3omega associates primarily with the CD3deltaepsilon complex; 2 ) CD3omega is not associated with single Tialpha or Tibeta chains, but is present in complexes composed of both the CD3 and the Ti chains; 3 ) CD3omega is part of the complete, intracellular receptor complex Tia lphabeta/CD3gammaepsilondeltaepsilonomegazeta2; and 4) CD3omega dissoc iates from the Ti/CD3 complex in the ER before maturation of the Tialp habeta heterodimer. On the basis of these results, we propose a model for the assembly and subunit stoichiometry of the TCR complex which in cludes the participation of the CD3omega chain.