A targeting vector was designed to replace the first exon of the targeted gene with a cre cDNA sequence and an frt-flanked PGK-neo cassette. The construct was electroporated into 129X1/SvJ-derived RW4 embryonic stem (ES) cells. Chimeric mice were bred to generate mutant mice. Mutant mice were then bred to FLPe mice (C57 genetic background) to remove the selection cassette. (J:90391)