Structure of hPol η. a. The ternary complex of hPol η with a normal DNA. Protein domains are shown in distinct colors and labeled. The DNA template is colored orange and the primer yellow. Oxygen and nitrogen atoms are colored red and blue, respectively. dAMPNPP is shown as stick-and-balls, and Mg2+ as purple spheres. All structural figures were made using PyMOL (www.pymol.org). b. The active site. Mg2+ coordination is indicated by pale yellow dashed lines. The 3´-OH of the primer strand is 3.2Å from the α-phosphate as indicated by the red dashed line. c. hPol η-DNA interactions around the active site. Protein side chains from the finger and palm domain are shown as light blue and pink sticks, respectively. d. Interactions with the upstream DNA. LF (shown as light purple ribbon diagram) contacts both template and primer, and the thumb domain (shown in green) only makes 3–4 hydrogen bonds with the primer strand. Side chains that make DNA contacts are highlighted in sticks and labeled.