Relaxed mutants of Escherichia coli RNA polymerase.

Unusual guanosine nucleotides synthesised during amino acid or energy source starvation are thought to be the effectors of the stringent response. In vitro experiments suggest that the magic spot compounds alter transcription specificity of RNA polymerase by binding to the enzyme. However, there is no good in vivo evidence for such an interaction. We define sites on the beta-subunit of RNA polymerase which, when altered, yield E.coli mutants apparently insensitive to the presence of ppGpp.