σB, 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 σB through a collection of regulatory kinases and phosphatases (the Rsb proteins) which catalyze the release of σB from an anti-σB 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 σB 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 σB. B. subtilis strains resistant to the antibiotic thiostrepton, due to the loss of ribosomal protein L11 (RplK), were found to he blocked in the stress activation of σB. Neither the energy-responsive activation of σB nor stress-dependent chaperone gene induction (a σB-independent stress response) was inhibited by the loss of L11. The Rsb proteins required for stress activation of σB 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 σB and suggest that the ribosomes may themselves be the sensors for stress in this system.
ASJC Scopus subject areas
- Molecular Biology