Synthesis of a defective H-2 histocompatibility antigen by mutant mouse strain BALB/c-H-2dm2

Mutant mouse strain BALB/c-H-2dm2 (dm2), which fails to express the H2Ld histocompatibility antigen associated with the wild type, BALB/c, synthesizes instead a smaller molecule that is structurally related to H-2Ld but does not carry detectable alloantigenic determinants. This new protein, p40, is a membrane glycoprotein found in dm2 cells but not in BALB/c. p40 was detected by electrophoresis of dm2 glycoprotein preparations and by immunoprecipitation with heterologous H-2-specific antibodies. The p40 molecule is found associated with intracellular membranes but was not detected at the cell surface. Peptide mapping studies suggest that dm2 carries an alteration in the H-2Ld structural gene, which prevents proper maturation of the protein product.