Promoter collections can be readily characterized via Relative Promoter Units (RPUs). The five promoters labeled J23### are from a constitutive promoter library and R0040 and R0011 are tet- and lac-repressible promoters, respectively. The activity of the promoters was measured in relative promoter units (RPUs). This collection of promoter may itself be useful for tuning gene expression in engineered systems. The error bars represent the 95% confidence interval of the mean based on nine replicates.