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Journal of Bacteriology, February 2006, p. 1286-1294, Vol. 188, No. 4
0021-9193/06/$08.00+0     doi:10.1128/JB.188.4.1286-1294.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Sll1717 Affects the Redox State of the Plastoquinone Pool by Modulating Quinol Oxidase Activity in Thylakoids

Galyna I. Kufryk^* and Wim F. J. Vermaas

School of Life Sciences and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-4501

Received 31 August 2005/ Accepted 23 November 2005

A Synechocystis sp. strain PCC 6803 mutant lacking CtaI, a main subunit of cytochrome c oxidase, is not capable of growing at light intensities below 5 µmol photons m^–2 s^–1, presumably due to an overreduced plastoquinone pool in the thylakoid membrane. Upon selection for growth at light intensities below 5 µmol photons m^–2 s^–1, a secondary mutant was generated that retained the CtaI deletion and had fully assembled photosystem II complexes; in this secondary mutant (pseudorevertant), oxygen evolution and respiratory activities were similar to those in the wild type. Functional complementation of the original CtaI-less strain to low-light tolerance by transformation with restriction fragments of genomic DNA of the pseudorevertant and subsequent mapping of the pseudoreversion site showed that the point mutation led to a Ser186Cys substitution in Sll1717, a protein of as-yet-unknown function and with a predicted ATP/GTP-binding domain. This mutation caused a decrease in the plastoquinone pool reduction level of thylakoids compared to that observed for the wild type. Based on a variety of experimental evidence, the most plausible mechanism to cause this effect is an activation of plastoquinol oxidation in thylakoids by the quinol oxidase CydAB that occurs without upregulation of the corresponding gene and that may be caused by an increased CydAB activity in thylakoids, conceivably due to altered CydAB sorting between cytoplasmic and thylakoid membranes. Sll1717 appears to be unique to Synechocystis sp. strain PCC 6803 and has a close homologue encoded in the genome of this organism. The transcript level of sll1717 is low, which suggests that the corresponding protein is regulatory rather than structural.

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* Corresponding author. Mailing address: School of Life Sciences and Center for the Study of Early Events in Photosynthesis, Arizona State University, Box 874501, Tempe, AZ 85287-4501. Phone: (480) 965-3698. Fax: (480) 965-6899. E-mail: Galyna.Kufryk{at}asu.edu.

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Journal of Bacteriology, February 2006, p. 1286-1294, Vol. 188, No. 4
0021-9193/06/$08.00+0     doi:10.1128/JB.188.4.1286-1294.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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