The full sequence of the Thy-1 membrane glycoprotein of rat brain is reported. The sequence was determined from tryptic and V-8 proteinase peptides and consisted of 111 amino acids. The amino terminus was blocked and consisted of a pyroglutamic acid residue. The molecule contained two disulphide bonds, namely Cys-9--Cys-111 and Cys-19--Cys-85. Three N-linked amino sugars were located at Asn-23, Asn-74 and Asn-98. In each case the sequence on the C-terminal side of the attachment point was Asn-Xaa-Thr as would be expected for N-linkage. The C-terminal peptides were unusual, in that they were either obtained in a highly aggregated form, or could only be purified after binding to Brij 96 micelles. Thus they appeared to have hydrophobic properties, yet did not contain any extended sequence of hydrophobic amino acids. Other unusual features of the C-terminal peptides were the presence of unidentified ninhydrin-positive material and of glucosamine and galactosamine. The C-terminal residue has not been directly identified but Cys-111 is the last conventional amino acid. It is suggested that the hydrophobic properties of the C-terminal peptides may be due to the linkage of lipid. The sequence of the Thy-1 glycoprotein showed homologies with immunoglobulin domains. This relationship is examined in detail in the paper following [Cohen et al. (1981) Biochem. J. 193, 000--000].

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