Abstract
Transcription of the rbcLS operon, encoding RuBisCO, is activated under low-CO2 conditions in the cyanobacterium Synechococcus sp. PCC 7942. We found three potential CbbR recognition sites in the upstream region of rbcL, two of which were shown to be essential for the low-CO2 responsiveness of the promoter. Two CbbR homologues (CmpR and RbcR) have been identified in Synechococcus. The expression level of the rbcLS operon in a cmpR-deficient mutant is higher than that in the wild-type strain, implying that RbcR is likely the regulator of the rbcLS operon. Since no rbcR-null mutant was obtained, we constructed an overexpression strain of Synechococcus, in which the rbcR gene is expressed from a nitrogen-regulated promoter. This strain showed a 2-fold increase in the expression level of rbcLS under the induction conditions. These results suggested involvement of RbcR in activation of the rbcLS operon in Synechococcus.
