Regulation of transcription from two ssrS promoters in 6S RNA biogenesis.

ssrS-encoded 6S RNA is an abundant noncoding RNA that binds σ(70)-RNA polymerase and regulates expression at a subset of promoters in Escherichia coli. It is transcribed from two tandem promoters, ssrS P1 and ssrS P2. Regulation of transcription from two ssrS promoters in 6S RNA biogenesis was examined. Both P1 and P2 were growth phase-dependently regulated. Depletion of 6S RNA had no effect on growth-phase-dependent transcription from either promoter, whereas overexpression of 6S RNA increased P1 transcription and decreased P2 transcription, suggesting that transcription from P1 and P2 is subject to feedback activation and feedback inhibition, respectively. This feedback regulation disappeared in Δfis strains, supporting involvement of Fis in this process. The differential feedback regulation may provide a means for maintaining appropriate cellular concentrations of 6S RNA.