Effect of SarA, agr and ArlR on esxA expression. A. Northern blot of esxA in Newman, and the ΔsarA (LR15), Δagr (KS186) and ΔarlR (SM99) mutants over growth. The ethidium bromide-stained 16S rRNA pattern is shown as an indication of RNA loading. B. Transcriptional activity of the esxA promoter in strain Newman (squares), ΔsarA mutant BS309 (stars/dots), Δagr mutant BS310 (triangles), and ΔarlR mutant SM99 (diamonds). Growth was followed by measuring the OD600 (open signs), and the activity of the esxA promoter-reporter construct was determined by the luciferase activity of pesxAp-luc+ (filled signs). The strains BS309 and BS310 are isogenic to LR15 and KS186, respectively, except for an exchanged resistance marker in the inactivated loci allowing the selection and maintenance of pesxAp-luc+ .