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Published on June 6, 2008; 10.1104/pp.108.122713

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Received May 9, 2008
Accepted May 28, 2008

Characterization of single and double inactivation strains reveals new physiological roles for group 2 sigma factors in the cyanobacterium Synechocystis sp. PCC 6803

Maija Pollari , Liisa Gunnelius , Ilona Tuominen , Virpi Ruotsalainen , Esa Tyystjarvi , Tiina Salminen , and Taina Tyystjarvi *

Plant Physiology and Molecular Biology, Department of Biology, University of Turku, FI-20014 Turku, Finland; Department of Biochemistry and Pharmacy, Abo Academi University, Biocity 3rd floor, FI-20520 Turku, Finland

* Corresponding author; email: taityy{at}utu.fi.

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 {sigma} factor of the RNA polymerase holoenzyme is responsible for the recognition of a promoter sequence. In the cyanobacterium Synechocystis sp. PCC 6803 the primary {sigma} 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 the present study we have used homology modeling to construct a three dimensional model of Synechocystis RNA polymerase holoenzyme and all group 1 and 2 {sigma} factors. According to the models, the overall three dimensional structures of group 1 and 2 {sigma} factors are similar, the SigB and SigD factors being the most similar ones. In addition, we have constructed a complete set of group 2 {sigma} factor double inactivation strains, {Delta}sigBC, {Delta}sigBD, {Delta}sigBE, {Delta}sigCD, {Delta}sigCE, {Delta}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 {Delta}sigBD strain, and all strains lacking the SigD factor were found to be sensitive to bright light. Furthermore, all group 2 {sigma} factors were found to be involved in acclimation to salt- or sorbitol-induced osmotic stresses.




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 J. Bacteriol.Home page
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.
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