This allele is similar to Catnnb1tm1(Nfkbia)Rsu in that an Nfkbia cDNA encoding amino acids 71 through 317 was inserted at the start codon of Catnnb1, but in this case, a floxed stop cassette preceded the Nfkbia sequence, precluding its expression. As in Catnnb1tm1(Nfkbia)Rsu, the coding region of the first coding exon and the following 4 downstream exons were deleted.