FIG 2.

Genetic evidence suggests that decreased expression of ClpC in a ΔsrrAB strain results in sensitivity to puromycin. (A) ClpC is required for puromycin resistance, while ClpL is dispensable. Growth for the WT (JMB 1100), ΔclpC (JMB 8025), and clpL::Tn (JMB 4850) strains is displayed on solid TSB medium with or without puromycin. (B) The puromycin sensitivity phenotypes of the ΔsrrAB and ΔclpC mutations are not additive. Growth for the WT, ΔsrrAB (JMB 1467), ΔclpC, and ΔsrrAB ΔclpC (JMB 8027) strains is displayed on solid TSB medium with or without puromycin. (C) Overexpression of clpC suppresses the puromycin sensitivity phenotype of the ΔsrrAB strain. The growth profiles of WT and ΔsrrAB strains with either pEPSA5 (empty vector) or pEPSA5_clpC are displayed on solid TSB medium with or without puromycin. (D) Transcriptional activity of clpC is decreased, while that for spa is increased, in a strain lacking SrrAB. Transcriptional activities are displayed for the WT with pLL39 and the ΔsrrAB strain with pLL39 or pLL39_srrAB and simultaneously carrying a multicopy plasmid containing gfp under the transcriptional control of either the clpC or spa promoter. Data in panel D represent the averages from triplicate cultures and error bars represent standard deviations. Photographs shown in panels A, B, and C are representative of at least three independent experiments, and the numbers beneath each photograph denote the serial dilution that cells were removed from before plating. Where indicated, Student t tests (two tailed) were performed. *, P < 0.05.