T-Cell Receptor-Associated Transmembrane Adapter 1 (TRAT1) is a single-pass type III membrane protein. TRAT1 exists as a disulfide-linked homodimer and is strongly expressed in the thymus, and to a lesser extent in the spleen, lymph node, and peripheral blood lymphocytes. TRAT1 is phosphorylated on tyrosines by LCK or FYN upon TCR activation. Its function is to stabilizes the TCR (T-cell antigen receptor)/CD3 complex at the surface of T-cells.