A construct containing the Vcre gene driven by the CAG promoter was inserted into the intron of the Gt(ROSA)26Sor locus via homologous recombination in Wit 9 ES cells. VCre/VloxP is a site-specific recombination system, which was derived from plasmid p0908 of Vibrio sp. VCre is a recombinase that recognizes its own specific target sites (VloxP). (J:263660)