Recombineering methods were used to modify a BAC containing the Rfx6 gene and generate the targeting construct. Homologous recombination in ES cells resulted in the first 5 exons being replaced by and EFGP/cre fusion gene followed by an FRT-flanked neo cassette. The neo was subsequently removed by crossing mice carrying the disrupted allele with Actb-Flp mice. (J:156925)