Exons 3-5, encoding the Toll-IL-1 receptor (TIR) domain, were flanked by loxP sites. The frt-flanked neomycin resistance cassette was removed via flp-mediated recombination. When the floxed region is removed via cre-mediated recombination, splicing from exon 2 to exon 6 results in a frameshift mutation. (J:209373)