Following Cre-mediated recombination, cells of mice bearing this transgene randomly express one of three histone 3.3 fusion proteins joining different fluorescent markers to either wild-type or one of two dominant-negative mutant forms (arginine-->lysine at amino acid (aa) position 26 (R26K) or lysine-->arginine at aa 27 (K27R)) of the Drosophila melanogaster histone 3.3A protein, whose sequence is identical to the mammalian histones 3.3A and 3.3B. This is accomplished by Cre recombinase-mediated deletion of sequences between pairs of lox2272, loxN or loxP sites, one member of each pair located in a cluster between a CAG promoter and a triple poly[A] (STOP) signal and the other upstream of a cDNA encoding one of the HIS3.3A fusion proteins - HIS3.3A/EGFP, HIS3.3A*R26K/ECFP, or HIS3.3A*K27R/mCherry - followed by a poly[A] signal. A single frt site following the last poly[A] was included in the transgenic construct to allow flp recombinase-mediated deletion of all except the single remaining copy of the transgene in progeny of the multi-copy founder mouse. Expression of the fusion genes is driven by the CAG promoter, which includes the cytomegalovirus immediate early (CMV-EI) enhancer followed by a 1.3-kb DNA segment including the promoter, first exon and first intron of the chicken beta-actin gene, with the 3' splice junction sequence replaced by that of the rabbit hemoglobin beta gene. (J:239167)
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