Practice question

6S RNA is highly abundant ~184 nucleotide noncoding RNA accumulating during stationary phase and nutrient limitation in Escherichia coli that structurally mimics open promoter DNA bubble. Its conserved elongated duplex with central bulge and terminal loop fits within active site channel of sigma70 holoenzyme, specifically contacting beta, beta' subunits and sigma70 region 4.2. Sequestration globally downregulates transcription from strong sigma70 promoters, freeing core polymerase to associate with alternative sigma factors like sigmaS and sigma32. Upon nutrient upshift, 6S RNA serves as template for short product RNAs pRNA, causing conformational change releasing polymerase and restoring exponential growth transcriptional program rapidly.