A targeting vector was designed to replace exons 5-7 with an IRES-GFP-PGK-neo. The neo was removed via cre-mediated recombination. Absence of endogenous transcript was confirmed by RT-PCR. Fluorescence is more intense after excision by Tg(Prm-cre)58Og (129/Sv background) or by Tg(Sp3-cre)93Knw (C57BL/6 background). When allele is made congenic on 129 or C57BL/6 background, immune system phenotype is not altered by removal of PGK-neo or by background. (J:112394)