MOLECULAR-CLONING OF A T-CELL-SPECIFIC ADAPTER PROTEIN (TSAD) CONTAINING AN SRC HOMOLOGY (SH)-2 DOMAIN AND PUTATIVE SH3 AND PHOSPHOTYROSINEBINDING-SITES

Adapter proteins link catalytic signaling proteins to cell surface rec eptors or downstream effector proteins. In this paper, we present the cDNA sequence F2771, isolated from an activated CD8+ T cell cDNA libra ry. The F2771 cDNA encodes a novel putative adapter protein. The predi cted amino acid sequence includes an SH2 domain as well as putative SH 3 and phosphotyrosine binding interaction motifs, but lacks any known catalytic domains, The expression of the gene is limited to tissues of the immune system and, in particular, activated T cells. The protein expressed by F2771 cDNA in transfected COS cells is localized in the c ytoplasm. A polyclonal antiserum raised against an F2771-encoded pepti de reacts with a tyrosine-phosphorylated 52-kDa protein expressed in p hytohemagglutinin-stimulated peripheral blood mononuclear cells. The g ene is localized to chromosome 1q21, a region often found to be aberra nt in lymphomas. The T cell-specific expression and the rapid inductio n of mRNA expression upon receptor binding, as well as the lack of cat alytic domains in the presence of protein interaction domains, indicat e that the F2771 gene encodes a novel T cell-specific adapter protein (TSAd) involved in the control of T cell activation.