A loxP site was inserted upstream of exon 5. An FRT-flanked neomycin resistance cassette with a 3 loxP site was inserted downstream of exon 7. Cre-mediated recombination removed the selection cassette, exon 6 and exon 7. These exons encode the conserved motif IV and V (helix-hairpin-helix region for DNA binding). Western blot analysis confirmed the absence of full-length and truncated version of the protein in testes. (J:212610)