This mutation, identified in a screen of G3 progeny of ENU treated mice for responses to various toll-like receptor ligands, is an A-to-G transition resulting in replacement of tyrosine with cysteine at amino acid 116 (Y116C), between the death domain (aa 19-109) and the toll-interleukin 1 receptor (TIR) domain (aa 160-296) of the protein.