Mechanism of transcriptional activation by a LysR-type transcriptional regulator CmpR

Abstract

In Synechococcus elongatus PCC 7942, the LysR-type transcriptional regulator CmpR activates transcription of the genes involved in the CO₂-concentrating mechanism (CCM) , including the cmpABCD operon and the sbtA gene, which encode the ABC-type high-affinity HCO₃^- transporter BCTI and the Na⁺-dependent high-affinity HCO₃^- transporter, respectively. Low concentration (~10μM) of 2-phosphoglycolic acid (2-PG), the product of the oxygenase reaction of RubisCO, enhances the binding of CmpR to the upstream region of the target genes, thus, suggesting that 2-PG is a co-inducer of CmpR (Nishimura et al,. 2008). In previous studies, we identified several 2-PG dependent CmpR-binding sites in the regulatory region of the cmpABCD operon. In this study, we found that 600μM of D-riburose-1,5-bisphosphate (RuBP) also enhances the binding of CmpR to each of these sites. This indicates that CmpR binds to the same sets of DNA sites in response to 2-PG and RuBP, suggesting that accumulation of RuBP would enhance the low-CO₂ responsive activation of the cmpABCD operon.