A loxP site was inserted upstream of exon 3, and a pgk-neo cassette flanked by FRT sites as well as a second loxP site were targeted downstream of exon 7. Chimeric mice were produced from two recombinant ES cell clones. Exons 3-7 were excised by Cre mediated recombination. Western blot, immunostaining and RT-PCR showed no protein or RNA were detectable in the mutant testis. (J:156018)