Molecular cloning of the cDNA encoding the T3 gamma subunit of the mouse T3/T cell antigen receptor complex

Complementary DNA (cDNA) clones encoding the T3 gamma subunit of the mouse T3/T cell antigen receptor complex were isolated from a cDNA library prepared from a cytochrome C-specific, I-E (class II antigen)-restricted murine T cell clone. The cDNA hybridized to a single mRNA transcript of 1 kb in size the expression of which was restricted to T lymphocytes. The 182-amino acid sequence deduced from the cDNA revealed a signal peptide, a 89-amino acid extracellular domain with one N-glycosylation site, a hydrophobic domain with a centrally located glutamic acid residue, and a 44-amino acid intracellular domain. Comparative analysis of the mouse T3 gamma sequence with those of the human T3 gamma chain and the related human and mouse T3 delta chains revealed that the regions incorporating the extracellular cysteine residues were highly conserved. More importantly, the mouse T3 gamma subunit retained the potential serine phosphorylation site (Ser 126) unique to the human T3 gamma subunit, in the membrane-proximal region of the intracellular domain. The 16-amino acid region flanking Ser 126 was totally conserved (100%) in the gamma subunits, yet showed little homology (38 to 44%) with the corresponding region in the delta subunits, in spite of the otherwise high degree of conservation (61 to 68%) between the remainder of the cytoplasmic domains of the gamma and delta chains.