Loss of Ribosomal Protein L11 Blocks Stress Activation of the Bacillus subtilis Transcription Factor ς B

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Abstract
ς B , the general stress response sigma factor of Bacillus subtilis , is activated when the cell's energy levels decline or the bacterium is exposed to environmental stress (e.g., heat shock, ethanol). Physical stress activates ς B through a collection of regulatory kinases and phosphatases (the Rsb proteins) which catalyze the release of ς B from an anti-ς B factor inhibitor. The means by which diverse stresses communicate with the Rsb proteins is unknown; however, a role for the ribosome in this process was suggested when several of the upstream members of the ς B stress activation cascade (RsbR, -S, and -T) were found to cofractionate with ribosomes in crude B. subtilis extracts. We now present evidence for the involvement of a ribosome-mediated process in the stress activation of ς B . B. subtilis strains resistant to the antibiotic thiostrepton, due to the loss of ribosomal protein L11 (RplK), were found to be blocked in the stress activation of ς B . Neither the energy-responsive activation of ς B nor stress-dependent chaperone gene induction (a ς B -independent stress response) was inhibited by the loss of L11. The Rsb proteins required for stress activation of ς B are shown to be active in the RplK − strain but fail to be triggered by stress. The data demonstrate that the B. subtilis ribosomes provide an essential input for the stress activation of ς B and suggest that the ribosomes may themselves be the sensors for stress in this system.