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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Characterization of Single and Double Inactivation Strains Reveals New Physiological Roles for Group 2 Factors in the Cyanobacterium Synechocystis sp. PCC 6803^1,[W]

Plant Physiology and Molecular Biology, Department of Biology, University of Turku, FI–20014 Turku, Finland (M.P., L.G., I.T., V.R., E.T., T.T.); and Department of Biochemistry and Pharmacy, Åbo Academi University, FI–20520 Turku, Finland (T.S.)

Cyanobacteria are eubacteria that perform oxygenic photosynthesis like plants. The initiation of transcription, mediated by the RNA polymerase holoenzyme, is the main determinant of gene regulation in eubacteria. The factor of the RNA polymerase holoenzyme is responsible for the recognition of a promoter sequence. In the cyanobacterium Synechocystis sp. PCC 6803, the primary factor, SigA, is essential for cell viability. The SigB, SigC, SigD, and SigE factors show significant sequence similarity with the SigA factor but are nonessential. In this study, we have used homology modeling to construct a three-dimensional model of Synechocystis RNA polymerase holoenzyme and all group 1 and 2 factors. According to the models, the overall three-dimensional structures of group 1 and 2 factors are similar, the SigB and SigD factors being the most similar ones. In addition, we have constructed a complete set of group 2 factor double inactivation strains, sigBC, sigBD, sigBE, sigCD, sigCE, and sigDE. All double mutants grow well under standard conditions, but differences are observed in stress conditions. The transition from lag phase to exponential growth is slow in the sigBD strain, and all strains lacking the SigD factor were found to be sensitive to bright light. Furthermore, all group 2 factors were found to be involved in acclimation to salt- or sorbitol-induced osmotic stresses.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Taina Tyystjärvi (taityy{at}utu.fi).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.122713

^* Corresponding author; e-mail taityy{at}utu.fi.

Received May 9, 2008; accepted May 28, 2008; published June 6, 2008.

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				M. Pollari, V. Ruotsalainen, S. Rantamaki, E. Tyystjarvi, and T. Tyystjarvi Simultaneous Inactivation of Sigma Factors B and D Interferes with Light Acclimation of the Cyanobacterium Synechocystis sp. Strain PCC 6803 J. Bacteriol., June 15, 2009; 191(12): 3992 - 4001. [Abstract] [Full Text] [PDF]