The following elements were inserted, in order, 2 kb 5' of the Ubb gene by targeted recombination in 129-derived embryonic stem (ES) cells: CMV enhancer/beta-actin promoter (CAG), loxP site, beta-geo, 3 stop transcription sites, loxP site, Wnt11, rabbit beta-globin 3' UTR. (J:101977)