The σ~(70) subunit of RNA polymerase induces lacUV5 promoter-proximal pausing of transcription

摘要

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 lacUV5 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.