A loxP site was inserted upstream of exon 7 and a Frt-flanked neo cassette with 3' loxP sequence were inserted downstream of exon 7. Cre-mediated recombination was used in an attempt to remove the neo cassette and exon 7. However, RT-PCR shows the expression of a longer transcript than in wild-type mice and sequencing shows that exon 7 is not deleted in transcripts and instead exon 6 and loxP sequence are inserted between exon 7 and exon 8. The insertion induces frame-shift mutations and causes translation termination at the breakpoint. Western blotting confirmed absence of protein in the spleen and the lung, indicating a null allele. (J:223478)