244 bp of the gene promoter was deleted and a self-excising selection cassette was placed downstream of the gene. The deleted sequence included two of the three DNAse hypersensitive sites in the promoter and the gene transcription start site but left most of the CpG island intact. After recombination and generation of chimeric mice, the selection cassette excised itself in the male germline leaving behind a single loxP site. Heterozygous mice that inherit the deletion paternally do not express the gene transcript as determined by RNAse protection assay.