Figure 10. Regulatory architecture of the Caulobacter stress response systems.

Expression of the GSR EcfG-sigma factor, sigT (σ^T), and select genes in the GSR regulon is regulated as a function cell cycle phase. σ^T-dependent transcription can be induced by certain signals (e.g. hyperosmotic stress), but is unaffected by hydrogen peroxide. Transcription of the sRNA, GsrN, is activated by σ^T, and the cell cycle expression profile of gsrN is highly correlated with sigT and its upstream regulators. Transcription of the catalase/peroxidase katG is independent of σ^T. GsrN dependent activation of KatG protein expression is sufficient to rescue the peroxide survival defect of a ∆sigT null strain. GsrN convenes a post-transcriptional layer of gene regulation that confers resistance to peroxide and hyperosmotic stresses.