Primary structural studies of an H-2L molecule confirm that it is a unique gene product with homology to H-2K and H-2D antigens.

Radiochemical methodology has been used in the isolation and preliminary biochemical characterization of the murine H-2Ld major histocompatibility complex gene product. The radiolabeled molecule was isolated by immunoprecipitation from the glycoprotein fraction of detergent-solubilized H-2d tumor cells. Six major CNBr fragments were isolated from a papain fragment of this molecule; three of the fragments are connected by disulfide bonds. Due to the high degree of homology between major transplantation antigens, it was possible to align the fragments by comparison of their amino acid sequences to that of the H-2Kb gene product. Of the positions available for comparison between H-2Ld and H-2Kb, H-2Dd, and H-2Kd gene products, 61 out of 80 (78%), 45 out of 55 (82%), and 12 out of 15 (80%), respectively, are identical. Differences between the Ld and Kb and Dd molecules are distributed throughout the amino acid sequence. These data indicate that the H-2Ld gene product is a molecular species distinct from, but homologous to, the H-2K and H-2D gene products.