The transgene contains the following elements: the CAG promoter, a loxP site, a neomycin resistance gene (including stop codon and poly(A) signal) a second loxP site, the human GCH1 cDNA with HA tag sequence coupled to it, and poly(A) signal sequence. This creates a conditional-ready allele that will express HA-tagged human GCH1 only after cre-mediated removal of the neo cassette. (J:223362)