A T2A cleavage peptide and the cre/ERT2 fusion protein-coding sequence were introduced to the 3'UTR of the mouse Th gene. An FRT-PGK-EM7-NEOpolyA-FRT-loxP cassette was placed downstream of the 3'UTR region. Homologous recombination was achieved in 129S6/SvEvTac-derived embryonic stem cells and resultant chimeric mice were crossed with Flp mice to excise the neomycin cassette. (J:239228)