Abstract
To downregulate gene expression in cyanobacteria, we constructed NOT gate genetic circuits using orthogonal promoters and their cognate repressors regulated translationally by synthetic riboswitches. Four NOT gates were tested and characterized in five cyanobacterial strains using fluorescent reporter-gene assays. In comparison to alternative systems used to downregulate gene expression in cyanobacteria, these NOT gates performed well, reducing YFP reporter expression by 4 to 50-fold. We further evaluated these NOT gates by controlling the expression of the ftsZ gene, which encodes a prokaryotic tubulin homologue that is required for cell division and is essential for Synechococcus elongatus PCC 7942. These NOT gates would facilitate cyanobacterial genetic engineering or the study of essential cellular processes.