The C. elegans tax-4 mutants are abnormal in multiple sensory behaviors: they fail to respond to temperature or to water-soluble or volatile chemical attractants. We show that the predicted tax-4 gene product is highly homologous to vertebrate cyclic nucleotide–gated channels. Tax-4 protein expressed in cultured cells functions as a cyclic nucleotide–gated channel. The green fluorescent protein (GFP)-tagged functional Tax-4 protein is expressed in thermosensory, gustatory, and olfactory neurons mediating all the sensory behaviors affected by the tax-4 mutations. The Tax-4::GFP fusion is partly localized at the sensory endings of these neurons. The results suggest that a cyclic nucleotide–gated channel is required for thermosensation and chemosensation and that cGMP is an important intracellular messenger in C. elegans sensory transduction.
