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

Abstract

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.

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Figure 4: Suppression of gene expression of PAC by RNAi.
Figure 1: Purification of the flavoprotein from isolated paraflagellar bodies.
Figure 3: Adenylyl cyclase activity of the flavoprotein purified from PFBs.
Figure 2: Sequencing of the Mr 105K and 90K polypeptides.

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Acknowledgements

We thank J. W. Hastings for critical reading of the manuscript, M. Ohmori and M. Ishiura for discussions, I. Nakashima and Y. Yamakawa for advice on subcellular fractionation, N. Murata for encouragement, Y. Makino for operation of the protein sequencer at NIBB Center for Analytical Instruments, and M. Itoh for technical assistance. Part of this work was done under the NIBB cooperative-research programme for the use of the Okazaki Large Spectrograph. This work was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan, and by Grants for Ground Research for Space Utilization from the Japan Space Forum. M.I. thanks NIBB and BRAIN for a postdoctoral fellowship during part of this study.

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Correspondence to Masakatsu Watanabe.

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Iseki, M., Matsunaga, S., Murakami, A. et al. A blue-light-activated adenylyl cyclase mediates photoavoidance in Euglena gracilis. Nature 415, 1047–1051 (2002). https://doi.org/10.1038/4151047a

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