A floxed PGK-neomycin resistance gene was inserted into intron 8 and an additional loxP site was placed in intron 7, 75 bp from the start of exon 8. Both exon 8 and the neomycin gene were subsequently removed from correctly targeted ES cells by Cre-mediated recombination. A frame shift mutation is predicted at the splice site between exon 7 and exon 9 in the resulting transcript.