Abstract
It is widely known that UV irradiation and reactive oxygen species result in damages of DNA molecule, which are reverted by various repair mechanisms. Due to unavoidable stresses in oxygenic photosynthesis, plants and cyanobacteria are supposed to develop the various repair systems, although they have been poorly understood at the molecular level. In this study, the role of lexA-like gene (sll1626) in Synechocystis sp. PCC 6803 was analyzed by DNA microarray, since lexA is one of the key components of SOS response in E. coli and other heterotrophic bacteria. Expressions of several genes including recA, umuC and sulA, which are under strict control of LexA in E. coli, were hardly affected in the sll1626-disruptant of Synechocystis. By contrast, mRNA level of sll1626 itself and several other genes including sll1009, slr0179 and sll1765 was 5-8 fold enhanced in the mutant. Expression of sll1694 (pilA1), slr1667, slr1668, slr2015, slr2016, slr2017 and slr2018 was suppressed. The effects on sll1694 were also confirmed by Northern hybridization. In accordance with these results, twitching motility of cells was lost in the mutant as judged from colony morphology on agar plates. These suggest that LexA-like Sll1626 protein is a transcription factor for genes of the pilus structure while not for recA-related genes in cyanobacteria.
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