A plasmid in which the CAG (CAGGS) promoter drives the bacteriophage D6 site-specific recombinase (dre). This is followed by an IRES-puromycin sequence for selection. The linearized construct was electroporated into R1 ES cells, and single-copy clones were injected into 8-cell embryos. Germline transmission was obtained for one of these clones. (J:154134)