A targeting construct is designed to insert a loxP-flanked neomycin resistance cassette downstream of exon 1 of the gene. Mutations (AGCTTAA to AGCAAATT) were introduced in the 3' UTR, corresponding to the putative miR-155 (microRNA 155) target site, resulting in a non-sense mutation. Cre-mediated recombination removed the floxed neo cassette. (J:226678)