![Examples (A,B) of transcriptional activator complexes that distort DNA. (A) Dimeric EcmrR in complex with promoter DNA (cartoon inset, PDB-6XL6), remodels (58° kink) the promoter DNA to create the optimal promoter architecture for E. coli holoenzyme [σ70 (grey surface) RNAP (α2ββ′ω surface colour shown in shaded box)] to form the EcmrR-RPo (PDB-6XL5) [22]. (B) Overview of the E. coli class-1 CAP-TAC (PDB-6B6H). The cyclic adenosine 3′,5′-monophosphate receptor (CAP) protein dimer (dark blue and dark red, cartoon inset), binds its cognate DNA and αCTD of RNAP (green) to introduce three DNA kinks (33°, 55°, 21°). This results in a full 92° turn, optimally orienting the promoter DNA for σ70-RNAP to bind [31]. Examples of transcription factors that stabilise aspects of the transcription complex are shown in C and D. (C) Crl (dark orange cartoon) binds residues of the β′clamp (beige cartoon) on E. coli RNAP and alternative σ factor σS (grey cartoon) through a distinct interface (shown by spheres) in the left inset. This tethering action creates a Crl-σS-RNAP complex that binds alternate promoter DNA to form the Crl-σS-RPo complex (PDB-6OMF) shown to the right of the inset [32]. (D) WhiB7 (cyan, cartoon) is a transcriptional activator in Mycobacterium tuberculosis (Mtb) that binds an AT-rich ‘hook’ sequence of DNA (shown by arrow) and σA (cartoon inset). By binding the active Mtb RNAP holoenzyme (surfaces coloured as E. coli RNAP), it creates the WhiB7-RPo (PDB-7KIF) [34]. Examples of steric occlusion in transcriptional repressors are shown in E and F. (E) Three E. coli NanR dimers binds three GGTATA repeats to form a NanR-dimer3/DNA complex. Their close proximity allows intramolecular protein–protein interactions to stabilise the multimeric assembly (PDB-6WG7). The 70.5 kDa cryo-EM structure of dimeric NanR in complex with cognate DNA (PBD-6WFQ) [26]. (F) Streptococcus agalactiae (Stag) BusR binds palindromic promoter DNA as a tetramer to repress transcription (PDB-7OZ3) [27]. The 5′ and 3′ DNA strands have been annotated throughout.](https://port.silverchair-cdn.com/port/content_public/journal/biochemsoctrans/49/6/10.1042_bst20210674/1/bst-2021-0674c.02.png?Expires=1716464933&Signature=lhGJXdNc-Wm5CG9p4b7iHcEtKxZs7vl9ZjZVSPyhFRLkJtoZuEO8pwIwJ7fFpkY7sVGhZQYlD1Fl9POzEuAcEjQq5SUT27cvaYykC6puoBrVtOIolWyC~rACD4XIh~rx0jxyydWnPM~R1~bPkoQeWpcVsAsLs~ni7cw7IB4Du~4wXNeHpOCK0XSMF0xhRy60SNNtqfNJlDaIYZ5hbfsDcvGraZq6vPlO0H8tbey81SsA2QduBG0J0cStg7zRYvKOf-aG5fzHfpZjG7DPJNDmWFnbH-I~hfjOmxlX~bupDBcL~GQ8sRwEWXpRxiXHMy8JNkfw3aL2brboHghWZ7Go7Q__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA)
Examples (A,B) of transcriptional activator complexes that distort DNA. (A) Dimeric EcmrR in complex with promoter DNA (cartoon inset, PDB-6XL6), remodels (58° kink) the promoter DNA to create the optimal promoter architecture for E. coli holoenzyme [σ70 (grey surface) RNAP (α2ββ′ω surface colour shown in shaded box)] to form the EcmrR-RPo (PDB-6XL5) [22]. (B) Overview of the E. coli class-1 CAP-TAC (PDB-6B6H). The cyclic adenosine 3′,5′-monophosphate receptor (CAP) protein dimer (dark blue and dark red, cartoon inset), binds its cognate DNA and αCTD of RNAP (green) to introduce three DNA kinks (33°, 55°, 21°). This results in a full 92° turn, optimally orienting the promoter DNA for σ70-RNAP to bind [31]. Examples of transcription factors that stabilise aspects of the transcription complex are shown in C and D. (C) Crl (dark orange cartoon) binds residues of the β′clamp (beige cartoon) on E. coli RNAP and alternative σ factor σS (grey cartoon) through a distinct interface (shown by spheres) in the left inset. This tethering action creates a Crl-σS-RNAP complex that binds alternate promoter DNA to form the Crl-σS-RPo complex (PDB-6OMF) shown to the right of the inset [32]. (D) WhiB7 (cyan, cartoon) is a transcriptional activator in Mycobacterium tuberculosis (Mtb) that binds an AT-rich ‘hook’ sequence of DNA (shown by arrow) and σA (cartoon inset). By binding the active Mtb RNAP holoenzyme (surfaces coloured as E. coli RNAP), it creates the WhiB7-RPo (PDB-7KIF) [34]. Examples of steric occlusion in transcriptional repressors are shown in E and F. (E) Three E. coli NanR dimers binds three GGTATA repeats to form a NanR-dimer3/DNA complex. Their close proximity allows intramolecular protein–protein interactions to stabilise the multimeric assembly (PDB-6WG7). The 70.5 kDa cryo-EM structure of dimeric NanR in complex with cognate DNA (PBD-6WFQ) [26]. (F) Streptococcus agalactiae (Stag) BusR binds palindromic promoter DNA as a tetramer to repress transcription (PDB-7OZ3) [27]. The 5′ and 3′ DNA strands have been annotated throughout.