LoxP sites were inserted to flank exon 22, which encodes the majority of the RNase III domain. Loss of this exon would result in the generation of in-frame stop codons generated by frameshift mutations, likely to destabilize the resulting transcript. Flp mediated recombination removed an FRT-flanked neo that was included in the vector. Cre-mediated recombination removed exons 22. (J:243335)