An inspection of the Schizosaccharomyces pombe genome database revealed that this eukaryotic microorganism possesses a gene that may encode a bacterial type of histidine-to-aspartate (His-Asp) phosphorelay component, namely, a response regulator. The predicted gene, named prr1(+) (S. pombe response regulator), encodes a protein that contains a typical phospho-accepting receiver domain, preceded by a mammalian heat shock factor (HSF)-like DNA-binding domain. Inactivation of this prr1(+) gene resulted in mutant cells defective in some aspects of stress responses, including sensitivity to oxidative stress, cold-temperature, and heavy metal toxicity. It was also demonstrated that Prr1 is required for the transcription of some genes (e.g., trr1(+), ctt1(+)), which are induced by oxidative stress. These results suggest that a His-Asp phosphorelay system may be involved in a stress-activated signaling pathway in S. pombe.