The σ70 subunit of RNA polymerase induces lacUV5 promoter-proximal pausing of transcription

The σ 70 subunit of Escherichia coli RNA polymerase (RNAP) is a transcription initiation factor that can also be associated with RNAP during elongation. We provide biochemical evidence that σ 70 induces a transcription pause at the lac UV5 promoter after RNAP has synthesized a 17-nucleotide transcript. The σ 70 -dependent pausing requires an interaction between σ 70 and a part of the lac repressor operator sequence resembling a promoter −10 consensus. The polysaccharide heparin triggers the release of σ 70 from the paused complexes, supporting the view that during the transition from initiation to elongation the interactions between σ 70 and core RNAP are weakened. We propose that the binding and retention of σ 70 in elongation complexes are stabilized by its ability to form contacts with DNA of the transcription bubble. In addition, we suggest that the σ 70 subunit in the elongation complex may provide a target for regulation of gene expression.