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Figure 4.
Figure 4. Structural Comparison of the Binary DNA and
Ternary Substrate Complexes of DNA Polymerase b with an A-A
Mismatch at the Boundary of the Active Site
A comparison of
the polymerase and DNA conformations near the polymerase active
site in the crystallographic structures of the binary (blue) and
ternary (green) complexes with an A-A mismatch (yellow) at the
primer terminus. As with matched termini, the N subdomain is
observed to be open in the binary complex and closed in the
ternary complex. Three striking conformational changes in the
DNA are observed in forming the closed ternary substrate
complex: (1) the adenine at the primer terminus rotates into a
syn-conformation; (2) this permits the templating adenine of the
mismatch to reposition itself opposite the primer terminus (n
-1); (3) the coding template cytosine (orange) flips into the
DNA helix, thereby forming Watson-Crick hydrogen bonds with the
incoming dGTP (orange).
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