This section of the supporting online material for Elowitz et al.'s report details the materials and methods used in their study. It describes the construction and integration of plasmids expressing CFP or YFP (wild-type codons) from various promoters, including P_LacO1 and λ P_R, into the chromosomal loci of E. coli strains via homologous recombination. The methods for measuring the expression levels of these fluorescent proteins, including statistical analysis and image acquisition, are outlined. The authors also provide a map of the E. coli chromosome, indicating the locations of the origin of replication and the cfp and yfp loci, chosen to avoid systematic differences while remaining sensitive to stochastic variations. Additionally, the section includes references to key literature and notes on the experimental procedures.This section of the supporting online material for Elowitz et al.'s report details the materials and methods used in their study. It describes the construction and integration of plasmids expressing CFP or YFP (wild-type codons) from various promoters, including P_LacO1 and λ P_R, into the chromosomal loci of E. coli strains via homologous recombination. The methods for measuring the expression levels of these fluorescent proteins, including statistical analysis and image acquisition, are outlined. The authors also provide a map of the E. coli chromosome, indicating the locations of the origin of replication and the cfp and yfp loci, chosen to avoid systematic differences while remaining sensitive to stochastic variations. Additionally, the section includes references to key literature and notes on the experimental procedures.