Negative control of rpoS expression by phosphoenolpyruvate: carbohydrate phosphotransferase system in Escherichia...

The sigma(S) (or sigma(38)) subunit of RNA polymerase, encoded by the rpoS gene, is a crucial regulator in the transcriptional control of a set of genes under stressful conditions, such as nutrient starvation. The expression of rpoS is regulated in a complex manner at the levels of transcription, translation, and stability of the product. Although a number of factors involved in the regulation of rpoS expression have been identified, the underlying molecular mechanisms are not fully understood. In this study, we identified the Crr (or EIIA(Glc)) protein as a novel factor that plays an important role not only in the transcriptional control but also in the translational control of rpoS expression. Crr is an important component in glucose uptake through the well-characterized phosphoenolpyruvate:carbohydrate phosphotransferase system. The results of a series of genetic analyses revealed that Crr negatively controls rpoS translation and transcription. The observed transcriptional control by Crr appears to be mediated by cyclic AMP. However, it was found that Crr negatively controls rpoS translation rather directly. These results suggest a possible linkage between the control of rpoS expression and carbon metabolism.