Both the Cd1d1 gene and the adjacent Cd1d2 gene were mutated in this allele. The coding sequence of Cd1d1 was replaced with a neomycin selection cassette and the coding sequence of Cd1d2 was deleted; however, the intergenic sequence was retained. Flow cytometric analysis on thymocytes derived from homozygous mice confirmed that no stable encoded protein was expressed on the cell surface. (J:47769)