The otiose mutation, which was identified in an ENU mutagenesis screen for mutants with altered responses to Toll-like receptor (TLR) ligands, corresponds to a T to C transition at nucleotide position 1095 of the gene, in exon 9 of 12 total exons. No immunoreactive protein is detected by western blot analysis of mutant macrophages, and immunoprecipitated protein from mutant macrophages exhibits no kinase activity in vitro.