An AAA to GCA mutation in exon 3 at nt 216, causing an K72A substitution was knocked in to the locus. A cassette containing a loxP-flanked ACN cassette containing Cre-recombinase under the control of the testes-specific promoter and a neo cassette was inserted downstream of the polyA signal. Excision of the cre-neo cassette occurred upon passage through the male germ line. (J:98949)