E2-Orange and E2-Red/Green show relatively mild phototoxicity. (A) E. coli cells were treated for 4 h with 1 mM IPTG to express either no FP (Control) or the indicated FP. Cells were then illuminated through a Texas Red (535–585 nm) filter for 15 min. In parallel, identical samples were not illuminated. Cells were then plated and grown overnight, and the percent survival was calculated based on colony number for the illuminated versus non-illuminated samples. Error bars represent s.e.m. (B) Quantitation of FP expression under the conditions of the phototoxicity experiment. Immediately before light treatment, aliquots of cells were taken for expression analysis. Whole-cell lysates were separated using SDS-PAGE followed by staining with Coomassie Blue.