V7, a novel leukocyte surface protein that participates in T cell activation. II. Molecular cloning and characterization of the V7 gene.

V7 is a cell surface glycoprotein expressed on Ag-activated T cells, monocytes, and granulocytes, as well as subpopulations of T cells and accessory cells present in thymic medulla and tonsil. A mAb directed against V7 inhibits the proliferative response of T cells to allogeneic cells or immobilized anti-CD3 Ab, but not lectin mitogens, suggesting that V7 plays a role in TCR/CD3-mediated T cell activation. We have used the anti-V7 Ab in eukaryotic expression cloning experiments to isolate a cDNA clone containing a 3,340-bp insert that encodes V7 when transiently expressed in simian and murine fibroblastoid cells. DNA sequence analysis revealed a novel 1,021-amino acid open reading frame the structure of which conforms to the category of type I integral membrane proteins. The protein sequence includes a 20-residue putative hydrophobic signal sequence followed by a putative extracellular domain of 934 amino acids, a prototypic hydrophobic transmembrane spanning a domain of 25 residues, and finally a short and highly charged putative cytoplasmic domain of 42 residues. The extracellular domain contains seven pairs of regularly spaced cysteine residues, suggestive of Ig-like domains. On the basis of statistical analysis of the sequences of the putative cysteine loops, all seven of the Ig-like domains belong to the variable, or V-type, category. By using fluorescence in situ hybridization, we have mapped the V7 gene to human chromosome Ip13. Thus, the V7 glycoprotein represents a novel member of the Ig superfamily that is involved in critical intracellular signals essential for immune function.