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Figure 2.
Figure 2: Models of closed and open complexes. a, Model of
the closed complex (minimal PIC). DNA template and non-template
strands are in blue and cyan, respectively. The TATA element is
in black and the nucleotide in the template strand that
represents position +1 in the open complex is shown as a
space-filling model. Top and bottom views are from the side and
front, respectively. b, Model of the open complex. c, Location
of nucleotides in DNA template strand initiator consensus
sequence and mutations influencing start site selection and DNA
opening. The open complex model is shown around the active
centre. Positions -8 and +1 of the template strand are labelled.
Position -8 lies adjacent to the B-reader helix that contains
residues important for TSS selection (Glu 62, Trp 63, Arg 64,
Phe 66, pale green spheres). The mobile B-reader loop
(green-yellow), which contains residues Arg 78 and Val 79
required for initial transcription and TSS selection, could
reach near positions -1 and +1. Sites of mutations abolishing
DNA opening in archaeal transcription are shown as salmon
spheres.
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