A loxP site was inserted upstream of exon 2 and a second loxP site was placed downstream of exon 3. A FRT-flanked Neo resistance cassette was placed further downstream of exon 3. The Neo cassette was excised in vivo using a CMV-Flp transgene, leaving one FRT site behind. Cre mediated recombination will excise exons 2 and 3, which encode 331 of the 354 amino acids of the Klf2 protein, including all three zinc fingers, the nuclear localization sequence, and >90% of the transactivation domain.