The cyanobacterium Synechococcus elongatus PCC 7942 is a potential photosynthetic cell-factory. In this study, two native promoters from S. elongatus PCC 7942 driving the expression of abundant cyanobacterial proteins phycocyanin (P cpcB7942) and RuBisCO (P rbc7942) were characterized in relation to their sequence features, expression levels, diurnal behavior, and regulation by light and CO2, major abiotic factors important for cyanobacterial growth. P cpcB7942 was repressed under high light intensity, but cultivation at higher CO2 concentration was able to recover promoter activity. On the other hand, P rbc7942 was repressed by elevated CO2 with a negative regulatory region between 300 and 225 bp. Removal of this region flipped the effect of CO2 with Rbc225 being activated only at high CO2 concentration, besides leading to the loss of circadian rhythm. The results from this study on promoter features and regulation will help expand the repertoire of tools for pathway engineering in cyanobacteria.
Keywords: CpcB promoter; diurnal rhythm; light-CO2 effect; promoter strength; rbc promoter.