We have cloned the gene encoding the TRPF and TRPC functions of Phycomyces blakesleeanus by complementation of the corresponding activities of Escherichia coli. TRPF also complemented a trpl mutation in Saccharomyces cerevisiae. As in other filamentous fungi, such as Neurospora and Aspergillus spp., the P. blakesleeanus TRPF and TRPC formed part of a trifunctional polypeptide encoded by a single gene (called TRP1). Transcription of TRP1 in P. blakesleeanus did not appear to be regulated by light or by the nutritional status of the culture. The information on the structure and organization of a P. blakesleeanus gene derived from these studies should be useful in devising molecular genetic strategies to analyze the sensory physiology of this organism.