A loxP site and an FRT-flanked phosphoglycerate kinase-neomycin (PGK-Neo) selection cassette were inserted upstream of exon 3 and a second loxP site downstream of exon 3. Cre-mediated recombination removed the PGK-Neo and exon 3. Western blot analysis confirmed absence of protein in MEFs and bone marrow derived macrophages. (J:257411)