LoxP sites were inserted upstream of exon 2 and downstream of exon 14 through homologous recombination. Cre-mediated recombination in ES cells resulted in the deletion of exons 2-14. The deletion resulted in the elimination of the N-deacetylase and N-sulfotransferase activities of the protein. RT-PCR analysis of cerebral RNA confirmed the absence of mRNA transcripts in homozygous mutant mice. (J:252046)