Evidence from cDNA clones that the rat leukocyte-common antigen (T200) spans the lipid bilayer and contains a cytoplasmic domain of 80,000 Mr

Abstract The leukocyte-common antigen (L-CA or T200) includes a family of lymphoid and myeloid cell surface glycoproteins with apparent molecular weights from 180,000 to 240,000. We report a partial protein sequence for thymocyte L-CA containing 1073 amino acids predicted from cDNA clones isolated using an oligonucleotide probe. Only one segment (residues 347–368) is likely to cross the membrane, and peptide data suggest that sequences N-terminal to this are outside the cell, with residues 369–1073 inside. The cytoplasmic domain includes possible phosphorylation sites and an internal homology between residues 385–671 and 676–986. Analysis of B lymphocyte cDNA clones suggests that B cell and thymocyte mRNAs are identical in 3′ sequences, but size differences in Northern blots suggest 5′ sequences may differ.