Interaction of σ70region 4 with -35 element DNA, the β-flap, AsiA and MotA. A) Sequence of σ70 Region 4 (residues 540-613) with subregions 4.1 and 4.2; the α helices H1 through H5 with a turn (T) between H3 and H4 are shown. Residues of σ70 that interact with the -35 element  are colored in magenta. Residues that interact with AsiA  or the region that interacts with MotA [97, 104] is indicated. B) Structures showing the interaction of T. aquaticus σ Region 4 with -35 element DNA  (left, accession # 1KU7) and interaction of σ70 Region 4 with AsiA  (right, accession # 1TLH). σ, yellow; DNA, magenta; AsiA, N-terminal half in black, C-terminal half in gray. On the left, the portions of σ that interact with the β-flap (σ residues in and near H1, H2, and H5) are circled in turquoise; on the right, H5, the far C-terminal region of σ70 that interacts with MotA, is in the green square. C) Structures showing the interaction of T. thermophilus σ H5 with the β-flap tip  (left, accession # 1IW7) and the structure of MotANTD  (right, accession # 1I1S) are shown. On the β-flap (left) and MotANTD (right) structures, hydrophobic residues (L, I, V, or F) and basic residues (K or R) are colored in gray or blue, respectively. The interaction site at the β-flap tip is a hydrophobic hook, while the structure in MotANTD is a hydrophobic cleft.