The resulting strain was named EMO3-C. This double reporter plasmid carries the complete Colicin E2 operon, but the genes cea and cel have been replaced by genes encoding the LY2109761 TGF-beta inhibitor fluorescence reporters YFP and CFP, respectively. In this double reporter plasmid, all regulatory elements for transcriptional, as well as for post-transcriptional regulation are present. This includes the SOS box for LexA binding, the transcriptional terminators T1 and T2, as well as the ribosome-binding site of cel and CsrA binding sites. Thus any regulatory mechanism, such as a probable colicin regulatory feedback, should not be affected in the double reporter plasmid, and the dynamics of fluorescent reporter expression may be assumed to directly reflect the dynamics of cea and cel gene expression. Using fluorescence time-lapse microscopy, we studied the parallel expression of YFP and CFP in individual bacterial cells. Cells were taken in the early exponential phase and subsequently analyzed either under natural conditions or in the presence of the SOS agentMitomycin C at various concentrations. To ensure that any differences in gene expression of the YFP and CFP reporter are not due to differences in theirmaturation times, we measured the maturation times of these fluorescence reporters in our strain EMO3-C, using a standard protocol. Both fluorescence proteinsmatured similar fast with a maturation time of less than 12 min, which is comparable to literature values and below the experimental resolution time of 15 min. Despite our expectations, we found the expression dynamics of the cea and cel gene to be very similar, if not identical in strain EMO3-C. This co-expression of the cea and cel gene could be observed for all applied MitC concentrations as well as for the un-induced case, indicating that a post-transcriptional regulation that is only affecting cel gene expression did not occur or is not detectable under the experimental conditions used in this study. To compare our time-lapse microscopy data with previous whole population studies in a quantitative way, we BAY 73-4506 introduced a threshold YFP or CFP fluorescence value that separated non-expressing cells with only low fluorescence intensities from highly expressing cells with high fluorescence values. These highly expressing cells were then considered to be in the ��ON�� state. The percentage of cells in the ��ON�� state for various concentrations of the SOS agentMitC at 75min after induction withMitC is shown in Fig. 2B. This timepoint was chosen, as whole population studies performed with strain EMO3-C revealed that for highMitC concentrations the maximum response could be observed at 75min after induction with this SOS agent.