Fig. 2
a FACS analysis of E. coli cells containing the synthetic nar promoter library. Histograms of sorted cell libraries and control cells are represented by colored lines. Black: negative control (empty vector), yellow: sorted cells showing weak intensities, green: positive control (a wild-type nar promoter), blue: sorted cells showing intermediate intensities, and red: sorted cells showing strong intensities. b Promoter strength analysis of the synthetic nar promoters. GFP fluorescence intensities of the collected 68 clones having synthetic nar promoters were measured by spectrofluorometer and normalized as relative fluorescence unit (RFU)/OD600. Representative strong (S3-2-64), intermediate (W2U-30), and weak (W2L-29) nar promoters are represented by green, yellow, and red bars, respectively