An IRES-lacZ gene replaced exons 3-7 via homologous recombination. An inserted neomycin cassette following the IRES-lacZ gene was removed. The insertion of the IRES-lacZ creates a premature termination and results in a peptide containing only the first 137 amino acids. Western blot analysis confirmed that no full-length protein is expressed in homozygous mice and immunofluorescence staining further confirmed absence of protein in embryos. (J:311848)