The targeting construct contained a cassette encoding an IRES-cre sequence followed by an frt-flanked neo selection marker. The construct was targeted to a position 3 nucleotides downstream of the Olfr157 coding sequence. After linearization the construct was injected into R1 ES cells. Clones were injected into C57BL/6J blastocysts and germline transmission was obtained. (J:154249)