Figure 8.

Crystal structure of a ternary polη•DNA•dCTP extension-stage complex. The polymerase active site (A) viewed from the major groove side of the DNA template–primer duplex and (B) rotated around the horizonal axis by 90°, viewed from the ceiling and along the base stack. The color code is identical to that in Figure 6. Nucleobase and sugar atoms of the 3′-terminal nucleotide of the primer strand, pG8, are highlighted in ball-and-stick mode to indicate partial occupancy of this residue. Calcium ions are shown as green spheres, and the putative nucleophilic attack of O3′(pG8) at the α-phosphate group is indicated with an arrow (A).