A targeting vector was generated using recombineering methods to modify a BAC containing the Slc26a5 (prestin) locus. An IRES-cre/ERT2-frt-neo-frt cassette was inserted after the stop codon in exon 20. The vector was electroporated into TL-1 ES cells to produce knockin mice. Mice were crossed with Tg(ACTFlpe)9205Dym animals to delete the neo cassette.