Genetic dissection of stringent control and nutritional shift-up response of the Escherichia coli S10 ribosomal protein operon.

The S10 operon of Escherichia coli is autogenously regulated by L4, one of 11 ribosomal proteins encoded by the operon. We have previously shown that L4 regulates transcription of the operon by modulating the level of read-through at an attenuator in the S10 leader. To determine the physiological roles of both L4-mediated attenuation and the regulation of transcription initiation, we have constructed mutations eliminating their two regulatory targets, the S10 leader and the S10 promoter. Our results indicate that stringent control requires only the S10 promoter and therefore is mediated at the level of initiation. However, growth-medium-dependent control after a nutritional shift-up involves regulation of both initiation of transcription at the promoter and transcription read-through at the attenuator.