presence of two putative transmembrane domains a putative 20 amino acid signal sequence and a 19 amino acid domain between residues 247 and 265 of the mature protein the sequence and its amino acid translation are shown in fig2 and fig1 a comparison with the amino acid sequence of the most similar molecules found in a search of genbank reveals clearly that it belongs to the immunoglobulin superfamily and the extracellular domain contains two ig c2 domain loops formed by two disulphide bridges it is a membrane crossing protein class one molecule with the n terminus at the exterior and traverses the membrane once the most closely related molecules belong to the natural killer receptor class which contains both inhibitory and activatory types gpvi clearly belongs to the activatory subclass not only through its function but also because unlike the inhibitory class it does not contain ltim sequences in its cytoplasmic domain neither does it contain any tyrosine residues which might be involved in phosphorylation there are some threonine and serine residues in this domain but they do not match any criteria for kinase consensus sequences like the activatory class of nk receptors gpvi contains an arginine residue as the third amino acid of the membrane crossing domain which is involved in the complex formation with the fc u03b3 subunit the cytoplasmic domain contains 51 amino acids showing only a minor similarity in the region just below the membrane to the cytoplasmic.