A human gene (LAR) that hybridizes to mouse leukocyte common antigen cDNA under relaxed hybridization conditions was isolated. The LAR gene is expressed in a broad range of cells, including T lymphocytes, kidney, and prostate cells. The structure of the protein encoded by the LAR gene was deduced by determining the nucleotide sequences of a 7.7-kb LAR cDNA. The putative LAR protein is composed of a 1,234 amino acid extracellular region, a 24 amino acid transmembrane segment, and a 623 amino acid cytoplasmic region. The cytoplasmic region contains two homologous domains that have extensive sequence similarity to the cytoplasmic region of the leukocyte common antigens. The NH2-terminal region of the extracellular segment of the LAR protein contains three tandem Ig-like domains and nine non-Ig-like domains. Among the known Ig-like proteins, the LAR protein has the highest degree of similarity to neural-cell adhesion molecule. The non-Ig-like domains of the LAR protein are also similar to the non-Ig-like domains of neural-cell adhesion molecule.

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