Abstract
Cyanobacteria possess a CO2-consentrating mechanism (CCM), which enables efficient uptake and assimilation of CO2. Some CCM-related genes (e.g. cmp opren, ndhF3 operon and sbtA) are activated under CO2-limited growth conditions. CmpR is a LysR family protein, which senses 2-phosphoglycolate (2PG) as a low CO2 signal and activates transcription of the cmp operon. Lately we found that CmpR binds to the ndhF3 promoter in a 2PG-independent manner, repressing ndhF3 operon transcription under high-CO2 conditions. The gene encoding CmpR (cmpR) is also repressed by CmpR under high-CO2 conditions and the short intergenic region upstream of cmpR was found to have a similar sequence to that of the 2PG-independent CmpR-binding site in ndhF3. EMSA analyses confirmed 2PG-independent binding of CmpR to this region. Moreover, EMSA revealed the presence of a second CmpR-binding site in the ORF located upstream of cmpR. The binding of CmpR to this site is observed in the absence of 2PG but was enhanced by 2PG. We are trying to identify the second binding site to gain insight into the self-regulation mechanism of cmpR.
