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Figure 5.
Figure 5. Mechanism of Tgt action. (a-c) Models of the
substrates (light green) corresponding to the three postulated
consecutive steps during NTP loading to the RNAP active site are
superimposed on the RNAP-Tgt structure; the E site (a), the
preinsertion site (b) and the insertion site (c); the PDB
accession codes used in panels a, b and c were 1R9T, 1Y77 and
1R9S, respectively. The putative coordination bonds with tMG
and/or cMG2 of Tgt (cyan), the NTP in the preinsertion site and
the  -phosphate
(P )
of the NTP in the insertion site (light green) (b,c), as well as
of the NTP  -phosphates
in the insertion site (c) in the 'catalytic' cP (yellow)
and 'inactive', tMG-bound tP (red)
configurations are shown by dashed lines. (d) Stabilization of
an inactive transcription intermediate by Tgt.
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