A neomycin cassette replaced 1.6 kb of the gene, from a portion of exon 2 to a portion of exon 6. The construct deleted the active site of the protein, Ser 93, located in exon 5. RT-PCR of total RNA from E13 gonads of homozygous mutant mice did not detect transcript. In addition, lack of protein in homozygous mutant mice was demonstrated functionally. (J:25249)