A targeting vector was designed to contain, from 5' to 3', a synthetic splice acceptor, a loxP site, an ATG start codon, a wildtype H3 histone isoform 3 (H3.3) coding sequence, H3f3b (H3 histone, family 3B) 3' UTR, and an SV40 polyadenylation (polyA) sequence. This was followed by a downstream frt-flanked neomycin resistance (neo) cassette, and a second loxP site, an ATG start codon, the cerulean variant of cyan fluorescent protein (CFP), and another SV40 polyA sequence. This vector replaced all of exon 2. Flp-mediated recombination removed the neo cassette. (J:194069)