Fig. 4: Detection of a mismatched base pair located in the postinsertion site.

a, Ribbon model of Pol ε cat in complex with mismatched substrate DNA and incoming nucleotide in the replication conformer. b, pol active site of Pol ε cat with a T–C mismatch at the postinsertion site. The cryo-EM density is shown as a mesh around the incoming ddATP and its templating nucleotide dT0, as well as for the mismatched base pair at the postinsertion site marked as dT-1 and dC-1. c, Superposition of the pol active site with a T–C-mismatched (as in b) or T–A-matched (gray) primer terminus in the postinsertion site. d, The mismatched T–C base pair in the postinsertion site. Dashed arrows demark distances (in Å) between indicated atoms. Here, distances between the nucleobase faces and between respective C1ʹ atoms are shown. e, View of the 3ʹ-terminal nucleotides of the nascent strand in the postinsertion (n-1) site, matched (left) or mismatched (right). Cryo-EM density is shown as a mesh around indicated side-chain residues, which are shown as sticks. Dashed lines indicate electrostatic and hydrogen-bond interactions between carboxyl groups of E858 and D860 in the Pol ε Palm domain and K954 of the Thumb domain.