Sequence encoding amino acid residues 2 to 126 were replaced with a neomycin resistance cassette, removing 124 of 147 residues, including all of the elements making up the active site. Northern blot confirmed absence of wild-type transcript in mutant testis, but showed the presence of a longer transcript resulting from transcription through the larger neomycin resistance cassette. Western blot demonstrated absence of protein in mutant testis. (J:100020)