Abstract
In cyanobacteria, small transcriptional regulators that consist solely of a helix-turn-helix motif of LuxR-family type are highly conserved. In Synechocystis sp. PCC 6803, a small LuxR-type regulator, Ssl0564, regulates the expression of several genes such as ndhD2 encoding a subunit of NAD(P)H dehydrogenase, rpe encoding pentose-5-phosphate-3-epimerase and katG encoding catalase-peroxidase when the reducing side of photosystem I is in oxidized state. It was revealed that purified Ssl0564 becomes dimeric form by the treatment with oxidizing agents and three cysteine residues at C-terminal region seem to be important for dimerization. The quantification of sulfhydryl groups of Ssl0564 using DTNB showed that oxidized and reduced form of Ssl0564 contain 0.15±0.11 and 3.14±0.32 mol of thiol/mol of the protein, respectively. We suppose that the activation of Ssl0564 is achieved by the formation of intra- and/or inter-molecular disulfide bonds at C-terminal three cysteine residues.
