Per3^{tm1.1(PER3)Sarc}

The targeting construct contained a cDNA sequence containing sequences of wild-type (WT) mouse exons 1821, with a downstream phosphoglycerine kinase (PGK) promoter driving a neomycin (Neo) selection marker. The sequence was flanked by locus of loxP sites and followed by the human exon 18, containing the 4-repeat allele of the human variable-number tandem-repeat (VNTR). Cre mediated recombination removed the cDNA encoding sequences contained in exons 1821, allowing the expression of humanized exon 18 with the 4-repeat copy of the human variable-number tandem-repeat (VNTR) and endogenous mouse exons 19-21. (J:222843)