PARENT SESSION
Posters P6B Photosynthetic acclimation: Mechanisms and gene expression. Abstracts (531-578)

ssl0564 is involved in a novel mechanism of redox regulation in Synechocystis sp. PCC 6803. Kinu Nakamura¹, Yukako Hihara^*,1, ¹ Department of Biochemistry and Molecular Biology, Saitama University, Saitama, Japan

ABSTRACT- ssl0564, a small ORF of a cyanobacterium Synechocystis sp. PCC 6803, was shown to encode the smallest member of the LuxR family of transcription regulators. Its 89-amino-acid sequence was similar over its entire length to the DNA binding domain of the LuxR protein family, including a putative helix-turn-helix motif. Purified Ssl0564 protein formed a dimer structure that could be disrupted to yield monomers by the addition of DTT or -mercaptoethanol. Three cysteine residues at the amino-terminal domain were well-conserved among cyanobacterial species and therefore seemed to be involved in dimerization through the formation of a intermolecular disulfide bond. In order to identify the target genes for Ssl0564, DNA microarray analysis of ssl0564-disrupted mutant was performed. It was revealed that chlL, chlN and chlB genes encoding subunits of light-independent protochlorophyllide reductase, katG encoding catalase-peroxidase and slr1957 were up-regulated and ssl0564-sll0296 operon, ndhD2 encoding a subunit of NADPH dehydrogenase and rpe encoding pentose-5-phosphate-3-epimerase were down-regulated by Ssl0564 under normal growth conditions. Regulation of transcript levels of these genes in response to changing light intensity was partially abolished in the ssl0564-disrupted mutant. These observations suggest that the dimeric form of Ssl0564 is involved in transcriptional regulation of these genes under oxidized conditions where cysteine sulfhydryl groups of Ssl0564 are oxidized to form disulfide bonds.

KEY WORDS: redox regulation, light environment, transcriptional factor, cyanobacteria