This mutation was identified in a screen of progeny of ENU mutagenized male mice for immunologic phenotypes. It is a C-to-A transversion in exon 5 (at nucleotide position 938 of cDNA sequence NCBI BC055453) that causes replacement of the neutral amino acid threonine with a charged lysine residue (T227K) in the fourth of six transmembrane domains. (J:100424)