The endogenous mouse gene was targeted using the RP24-297F14 bacterial artificial chromosome (BAC), from the RPCI-24 mouse genomic library derived from a C57BL/6J male mouse, in which the sequence from the translation initiation site through the 3' untranslated region (3'-UTR) had been replaced by the orthologous human sequence. A single FRT site ~1 kb downstream of the humanized 3'-UTR marks the location of a neomycin resistance cassette that has been removed by Flp recombinase. (J:342505)