Fluorescence images showing simultaneous expression of the cka-DsRed-Express2 and lexA-gfp transcriptional fusions. A:. Expression of cka-DsRed-Express2 gene fusion. B: Expression of lexA-gfp gene fusion in RW118. The arrow indicates a cell with high level expression of cka, but not lexA, showing that colicin activity gene expression can occur in the absence of the SOS response.