Fig. 2.

A representation of RNA polymerase holoenzyme-promoter interactions. (A) RNAP β and β′ subunits are indicated by green boxes. The RNAP α subunits (red circles and black arcs) are in contact with the bent upstream UP element. σ⁷⁰ (dark blue box) sub-region 4.2 (pale green), 3.0 (pale orange), 2.3/2.4 (pale purple), 1.2 (pale pink), and 1.1 are associated with the indicated −35 sequence (pale green), extended −10 sequence (pale orange), −10 sequence (pale purple), discriminator (pale pink), and double stranded DNA, respectively. In this case, promoter elements are separated by 17-bp. (B) RNAP holoenzyme promoter binding is obstructed (red arrow and a red cross) by DNA bending mediated by nucleoid structuring factors or transcription factors (purple ovals, circles, and lines), other transcription regulators (golden ovals with green hexagon ligands bound) bound to operator sequences (gold box), spacing greater than 17-bp between the −35 and −10 sequences, and a −35 sequence deviating from the canonical −35 sequence (yellow and red bars). These figures are modified from the work by Browning and Busby [121].