Fig. 2.

DNA polymerase replication fidelity filters. Shaded areas correspond to fidelity filters: preinsertion site (n, orange), insertion site (n, blue), catalytic site (magenta), postinsertion site (n-1, pink), and DNA duplex-binding region (n-2 to n-5, gray). DNA primer (copper) and template strands (orange) are also shown. The O helix transitions from an open (magenta) through an ajar (gray) to a closed (blue) conformation. Cognate-shaped base pairs (blue) are positioned for catalysis in the closed state. Noncanonical shapes (gray) tend to be selected against in the ajar conformation. The polymerase makes hydrogen bonds with the minor groove of base pairs positioned at sites n-1 to n-5 in the duplex-binding region following incorporation. This figure combines information derived from four structures: open (1L3U) (15), ajar (3HP6) (29), and closed (2HVI and 3EZ5) (34, 42).