Figure 2.

Overlapping promoters in the cbpA regulatory region. (A) Sequence of the cbpA regulatory region. Promoters for Eσ⁷⁰ (red) and Eσ³⁸ (blue) are highlighted. The transcription start sites are labelled with arrows and designated as ‘+1’. Note that, throughout this work, we have numbered all mutations in the cbpA regulatory region with respect to the Eσ⁷⁰ ‘+1’. (B) Open complex formation by Eσ³⁸ and Eσ⁷⁰. The panel shows the results of a KMnO₄ footprinting experiment designed to detect open complex formation by RNA polymerase at the cbpA regulatory region. The positions of DNA opening by Eσ³⁸ and Eσ⁷⁰ are highlighted in blue and red, respectively and the transcription start sites are shown by arrows. Eσ⁷⁰ was added in 3-fold excess of Eσ³⁸. (C) In vitro transcription by Eσ³⁸ and Eσ⁷⁰. The results of an in vitro transcription assay are shown. The lower band corresponds to the RNAI transcript, which acts as an internal control. The upper bands are transcripts that initiate from the cbpA regulatory region and are due to transcription by either Eσ³⁸ (blue) or Eσ⁷⁰ (red). Eσ⁷⁰ and Eσ³⁸ were added in equal amounts.