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Letters to Nature

Nature 415, 1047-1051 (28 February 2002) | doi:10.1038/4151047a; Received 28 September 2001; Accepted 7 January 2002

A blue-light-activated adenylyl cyclase mediates photoavoidance in Euglena gracilis

Mineo Iseki1,2,3, Shigeru Matsunaga4, Akio Murakami5, Kaoru Ohno1, Kiyoshi Shiga6, Kazuichi Yoshida1, Michizo Sugai7, Tetsuo Takahashi8, Terumitsu Hori4 & Masakatsu Watanabe1,10

  1. National Institute for Basic Biology, Okazaki, Aichi, 444-8585 Japan
  2. Bio-oriented Technology Research Advancement Institution, 3-18-19, Toranomon, Minato-ku, Tokyo, 105-0001 Japan
  3. Center for Gene Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602 Japan
  4. Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8572 Japan
  5. Kobe University Research Center for Inland Seas, Iwaya, Awaji, Hyogo, 656-2401 Japan
  6. Department of Physiology, Kumamoto University School of Medicine, Honjo, Kumamoto, Kumamoto, 860-8556 Japan
  7. Department of Biology, Faculty of Science, Toyama University, Toyama, Toyama, 930-8555 Japan
  8. School of Pharmaceutical Sciences, Toho University, 2-2-1, Miyama, Funabashi, Chiba, 274-8510 Japan
  9. Department of Photoscience, School of Advanced Sciences, Graduate University for Advanced Studies, Shonan Village, Hayama, Kanagawa, 240-0193 Japan

Correspondence to: Masakatsu Watanabe1,10 Correspondence and requests for materials should be addressed to M.W. (e-mail: Email: machakou@nibb.ac.jp).

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Blue light regulates processes such as the development of plants and fungi and the behaviour of microbes1, 2. Two types of blue-light receptor flavoprotein have been identified: cryptochromes, which have partial similarity to photolyases3, 4, and phototropins, which are photoregulated protein kinases5, 6. The former have also been found in animals with evidence of essential roles in circadian rhythms7, 8. Euglena gracilis, a unicellular flagellate, abruptly changes its swimming direction after a sudden increase or decrease in incident blue light intensity, that is, step-up or step-down photophobic responses, resulting in photoavoidance or photoaccumulation, respectively9. Although these photobehaviours of Euglena have been studied for a century10, the photoreceptor molecules mediating them have remained unknown9. Here we report the discovery and biochemical characterization of a new type of blue-light receptor flavoprotein, photoactivated adenylyl cyclase, in the photoreceptor organelle of Euglena gracilis, with molecular genetic evidence that it mediates the step-up photophobic response.