The targeting vector is designed with (from 5' to 3') a CMV-IE enhancer/chicken beta-actin/rabbit beta-globin hybrid promoter (CAAG), a loxP-flanked STOP/Neo cassette, SuperClomeleon (an improved fluorescent fusion protein containing Cerulean and YFP) and a polyA sequence. SuperClomeleon differs from Clomeleon by the following additions: a short interdomain linker, an S30R point mutation in both domains, intermediate affinity-tuning mutations, Q69T/V163A double mutant in YFP and replacement of the CFP domain with Cerulean. It provides a higher choloride sensitivity than Clomeleon. (J:316904, J:325762)