The targeting vector is designed with (from 5' to 3') the CMV-IE enhancer/chicken beta-actin hybrid promoter (CAG; from the pCAGGS vector), an FRT site, a STOP cassette flanked by loxP sites, a photoactivatable green fluorescent protein (PA-GFP) fused to the human histone H2B sequence, and a woodchuck hepatitis virus post-transcriptional regulatory element (WPRE; to enhance the mRNA transcript stability). (J:101977)