A novel sigma(E) regulated small RNA in Escherichia coli
The stationary phase and general stress alternative sigma factor σ S (RpoS) is regulated at multiple levels, including translational activation by two small regulatory RNAs. Out of a number of RNA modification mutants tested for a role in RpoS expression, a null mutation in miaA was shown to cause a defect in RpoS expression. Genetic experiments determined that MiaA is necessary for RpoS expression at the level of translation. In a separate portion of this work, the regulation of synthesis of the small RNA RybB was studied and found to be dependent upon the alternative sigma factor σE (RpoE). Increasing σE synthesis or activity led to a rapid and significant increase in the specific activity of a rybB-lacZ transcriptional fusion. Furthermore, both the activity of the rybB-lacZ fusion and the steady-state levels of the RybB RNA were undetectable in the absence of σ E. Genetic evidence suggested that RybB is only necessary for RpoS translation in the absence of RprA. To determine whether RprA affects rybB synthesis, the activity of the rybB-lacZ transcriptional fusion was measured in the absence of RprA and RybB. Surprisingly, the rybB-lacZ fusion increased only in the absence of RybB, suggesting that there is auto repression of RybB. This is the first demonstration of a σE regulated small RNA and adds a level of complexity to the σE regulon and the envelope stress response. This research also suggests that RybB and σE may be involved in an interesting auto-regulatory circuit.
0307: Molecular biology