Journal of Photoscience
- Volume 9 Issue 2
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- Pages.98-101
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- 2002
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- 1225-8555(pISSN)
Photactivated adenylyl cyclase, a novel blue-light receptor flavoprotein, mediates photoavoidance in the unicellular flagellate Euglena gracilis
- Iseki, Mineo (National Institute for Basic Biology,Bio-oriented Technology Research Advancement Institution,Center for Gene Research, Nagoya University) ;
- Matsunaga, Shigeru (Institute of Biological Sciences, University of Tsukuba) ;
- Murakami, Akio (Kobe University Research Center for Inland Seas) ;
- Ohno, Kaoru (National Institute for Basic Biology) ;
- Shiga, Kiyoshi (Department of Physiology, Kumamoto University School of Medicine) ;
- Yoshida, Kazuichi (National Institute for Basic Biology) ;
- Sugai, Michizo (Department of Biology, Faculty of Science, Toyama University) ;
- Takahashi, Tetsuo (School of Pharmaceutical Sciences, Toho University) ;
- Hori, Terumitsu (Institute of Biological Sciences, University of Tsukuba) ;
- Watanabe, Masakatsu (National Institute for Basic Biology, Dept. of Photoscience, School of Advanced Sciences, Graduate University)
- Published : 2002.08.01
Abstract
Euglena gracilis abruptly changes its swimming direction after a sudden increase or decrease in incident light intensity, that is, step-up or step-down photophobic responses, resulting in photoavoidance or photoaccumulation, respectively. To identify the photoreceptor molecules for these UV-A/blue-light type photobehaviors, we purified a flavoprotein from isolated putative photosencory organelles (PFBs) of Euglena. The purified flavoprotein, which noncovalently bound flavin adenine dinucleotide (FAD), seemed to be a heterotetramer of alpha- and beta-subunits. Predicted amino acid sequences of each of the subunits were similar to each other and contained two FAD-binding domains each followed by an adenylyl cyclase catalytic domain. The purified flavoprotein actually showed adenylyl cyclase activity, being drastically elevated by blue-light irradiation. Suppression of gene expression of the flavoprotein (Photoactivated Adenylyl Cyclase, PAC) by RNA interference (RNAi) caused loss of the step-up photophobic response, demonstrating that PAC actually mediates photoavoidance of Euglena.