Figure 2.

Comparison between the transcription initiation mechanisms of the primary σ⁷⁰ factor (RpoD) and the extracytoplasmic function σ factor (ECF) RpoE, from E. coli. (a) Involvement of the different σ factor domains (using the same color code as in Figure 1) in the transcription initiation, emphasizing the differences between the vegetative σ⁷⁰ factor and RpoE regarding their promoter melting capability. The different isomerization stages from closed complex to open complex are indicated. (b) Schematic of the contacts between -10 box nucleotides and σ₂ domain residues for RpoD and RpoE. Residues directly interacting with -10 box nucleotides are underlined. Nucleotides that are flipped-out during transcription initiation and the respective residues that contact them are indicated in red.