Exon 14 was disrupted by the insertion of a neomycin cassette. Sequence analysis of truncated transcript identified by Northern analysis, showed that an aberrant splice pattern resulted in the excision of exon 14. The joining of exons 13 and 15 resulted in a frameshift mutation which introduced a stop codon in exon 15, upstream of an essential peroxisomal targeting signal. Western analysis revealed an absence of normal protein in the livers of homozygous mutant mice.