A cassette containing codon improved cre (icre) and an FRT-flanked ampicillin resistance gene was inserted at the ATG site in the first exon in the Trpv1 gene in BAC RP23-292B23 containing the entire Trpv1 locus. The ampicillin gene was removed from the BAC construct by Flp expression. The purified BAC was microinjected into pronuclei of mouse oocytes. (J:167752)