Model of human TM and amino acid sequence of deleted amino terminal end for expression in COS.del.Nterm cells. Nascent human TM has 575 amino acid residues starting with a putative 18-residue signal peptide (S) at the N-terminal end. This is followed by 5 structural domains: (1) the N-terminal domain composed of a lectin-like module and a hydrophobic region (H-P), (2) six EGF-like repeats, (3) a serine-threonine (ST)-rich region, (4) the transmembrane domain (T), and (5) the cytoplasmic domain at the C-terminal. Numbering of amino acids is according to Suzuki et al.10 TM cDNA constructs lacking the encoding regions for the entire N-terminal domain (residues −17 to 238), the lectin-like module (residues 2-155 in pink), or the hydrophobic module (residues 161-202 in purple) were transfected for expression as COSdel.238 cells, COSdel.2-155, or COSdel.161-202 cells, respectively, as detailed in the Materials and Methods.