Fig. 5: Expression of monomeric mutants in E. coli cells elicits a range of phenotypes associated with Lon deficiency.
From: A 5+1 assemble-to-activate mechanism of the Lon proteolytic machine
a Pictures showing the colonial morphology of E. coli MG1655 cells transformed with the EcoLon-ΔN-E614K or -ΔN-L709R plasmids. Cells without induction by L-arabinose appear as non-mucoid colonies when cultured on agar media (left), but cells with protein overexpression induced by L-arabinose form mucoid colonies (right). b Images of MG1655 cells transformed with a control vector or plasmids expressing EcoLon-ΔN-E614K or -ΔN-L709R, without or with UV treatment. c Calculated cell-size distributions of the transformed MG1655 cells from the UV experiments in (b). The quantified region contains at least 500 cells, which were detected using a minimum cell area of 0.9 µm2. Four asterisks (****) denote P < 0.0001; the P-values approach zero. d UV sensitivity of transformed MG1655 cells. Cells expressing EcoLon-ΔN-E614K or -L709R were exposed to the indicated doses of UV irradiation at 254 nm. The P-values for ΔN-E614K at UV doses of 2, 5, and 10 mJ are 0.0035, 0.000021, and 0.00077, respectively; the corresponding P-values for ΔN-L709R are 0.025, 0.000038, and 0.0008, respectively. e Persister levels of transformed MG1655 cells treated with ofloxacin (OFX). Cells expressing EcoLon-ΔN-E614K or -L709R were treated with 5 μg/mL OFX for 0, 1, 2, 4, 6, and 24 h. The P-values for ΔN-E614K at 2, 4, and 6 h are 0.000072, 0.0052, and 0.0024, respectively; the corresponding P-values for ΔN-L709R are 0.000073, 0.0063, and 0.0032, respectively. CFU of cells treated with UV exposure (d) or OFX (e) were determined by plating on LB agar media with L-arabinose. The dashed line indicates the limit of detection for CFU counts. Data are presented as mean with SD (as shown by error bars) of three independent measurements. Statistical analysis was performed using one-way ANOVA with Tukey’s multiple comparisons test: *, **, and *** represent P < 0.1, P < 0.01, and P < 0.001, respectively; n.s. = not significant. Source data are provided as a Source Data file.
