The floxed neomycin selection cassette that had replaced the last two exons of the endogenous gene was excised from Cabin1tm1Che via in vivo cre mediated recombination. The deleted region encoded the carboxy terminal which includes the calcineurin, calmodulin, and MEF2 binding domains. Northern blot analysis of homozygous mutant mice identified a transcript of the anticipated size in brain and thymus tissue. While RT-PCR and subsequent sequence analysis showed that translation of this transcript could result in a truncated protein that contained 4 new amino acid residues in place of the endogenous carboxy terminal, the lack of an amino terminal antibody prevented direct confirmation of such a peptide.