The Cpg3 phenotype was identified in an ENU mutagenesis screen for mutants with impaired response to Toll-like receptor (TLR) ligands. The mutation is a T-to-A transversion at nucleotide position 747 of the gene (Genbank Accession NM_031178) that results in replacement of valine by glutamic acid at amino acid position 214 of the receptor protein. (J:128406)