The 45 bp (CTGTCACGGAAACCCCCACGTGTGATGGAAAGTCCAAAATTGTAC) Aire enhancer region within the conserved noncoding sequence 1 (CSN1) region, including two Nfkb1 binding sites, was replaced with a floxed neomycin resistance cassette. Cre-mediated recombination removed the selection cassette. (J:233730)