FIGURE 1.

The RNAP-binding σ-regulators and their interaction with RNAP. (A) Scheme of the main steps in transcription initiation. The steps regulated by RNAP-binding transcription factors (RPB-TFs) and DNA-binding transcription factors (DB-TFs) are indicated. (B) Basal promoter architecture (first described in E. coli) and interaction of its key elements with σ-domains. (C) Domain organization of the principal σ subunits and RbpA. NCR – non-conserved region, NTT – N-terminal tail, RCD – RbpA core domain, BL – basic linker, SID – σ-interacting domain. Alignment of the σ subunits from E. coli (Eco), M. tuberculosis (Mtb), C. crescentus (Ccr), C. trachomatis (Ctr), and T. thermophilus (Tth). Amino acid residues implicated in contacts with activators (bottom) are shown in color. (D) Schematic presentation of the RNAP holoenzyme structure with the binding sites for the activators and repressors targeting domains σ2 and σ4, respectively.