Identification Of The Co-inducer Involved In Low-CO₂ Activation Of The CmpABCD Operon By The LysR-type Transcriptional Regulator CmpR In The Cyanobacterium Synechococcus Elongatus

Abstract

The ABC-type bicarbonate transporter BCT1, which is encoded by the cmpABCD operon, is a component of the CO₂-concentrating mechanism (CCM) of cyanobacteria. The cmp operon of Synechococcus elongatus is activated under CO₂-limited conditions like other CCM-related genes. We previously reported that the low-CO₂ activation of the cmp operon requires CmpR, a LysR-type transcriptional regulator closely related to CbbR of photosynthetic and autotrophic bacteria. Three cis-acting elements were also identified in the cmp upstream region. In this study, we confirmed that CmpR binds to the cmp regulatory region and found that RuBP (>1mM) and 2-phosphoglycolate (>10μM) strongly enhance the CmpR binding to the DNA. Unlike CbbR of Rhodobacter capsulatus, CmpR did not respond to 3-phosphoglycerate. Given the involvement of O₂ in adaptive responses of CCM in cyanobacteria, our results suggest that 2-phosphoglycolate, which is generated by oxygenation of Rubisco, acts as the signal of CO₂-deficiency.