Characterization of inhibitors of tagging and proteolysis. Two mCherry-based reporters were used to determine which compounds inhibited tagging of nascent polypeptides and which inhibited proteolysis of tagged proteins. Schematic diagrams of the mCherry-trpAt reporter (A), and mCherry-tag reporter (D) indicate the conditions that produce fluorescent cells. Epifluorescence (mCherry panels) and DIC micrographs were used to measure the fluorescence in ΔssrA cells, ΔclpX cells, or in WT cells treated with DMSO only or with one of the compounds. Representative micrographs for mCherry-trpAt (B) and mCherry-tag (E) are shown. The fluorescence intensity in >330 individual cells was measured, and the cells were scored as positive if the intensity was >2 SDs higher than the average intensity for the DMSO-treated control. The percentage of positive cells for mCherry-trpAt (C) and mCherry-tag experiments (F) is shown. Compounds were added at 100 μM, with the exception of KKL-52 in C, which was added at 10 μM. Error bars indicate SDs.