Using BAC RP23-122N18, the first coding exon was replaced with a cassette containing the Fast Fluorescent Timer gene, poly(A) signal sequences and a loxP site flanked neomycin resistance gene cassette. The neo cassette was removed through subsequent cre-mediated recombination. The FT gene is a mutated form of mCherry (M18V E34K K69R L84W S149T A224S). (J:264610)