A loxP site was inserted into intron 3 and an FRT site flanked neomycin resistance gene cassette and a second loxP site into intron 5. Subsequently, the neo cassette was removed through flp-mediated recombination and exons 4 and 5 were deleted through cre-mediated recombination, leaving a null allele. RT-qPCR confirmed the absence or significant reduction in transcription from this allele. Western blots confirmed virtual absence of peptides translated from this allele. (J:239921)