Locations of the mutations in the PolG catalytic core with modeled primer template DNA. The four mutations under study are distributed throughout the structure of PolG catalytic core. Residue K601 is buried within the spacer-region (magenta) IP subdomain. Residue Y837 is located within a region between the exonuclease (purple) and polymerase domains (pink), at a distance of ~29 Å from the polymerase active site The location of Y831 on the surface of the enzyme at the opposite side of the thumb helices (H, I) from the putative DNA-binding channel excludes it from any direct interactions with the polymerase active site. D122 resides in the N-terminal region of the exonuclease domain, but it is much closer structurally to the polymerase domain and the polymerase active site. Residue Q1236 resides within the C-terminus of the PolG enzyme. Primer-template DNA was modeled onto the crystal structure of PolG (PDB:3IKM) using the bacteriophage T7 DNA polymerase crystal structure (PDB:1T8E) as a template.