Fig. 2.

Structure and cryo-EM density details of Rev3. a, Close-up view of the active site of Rev3 depicting key residues forming the T₀-P₀ binding site, including ligands and metal ions. Highlighted on the right is the well-resolved density for the T₀ and T₁ positions (red) and the sequence of the palindromic DNA employed to form the ternary complex. The region of the template-primer duplex enclosed in the box was built into the final model. b, Structure of Rev3 colored by domain. Dark blue, brown, magenta, cyan, yellow, orange and grey denote, respectively, the N-terminal, RIR, exonuclease, palm, fingers, thumb, and C-terminal domains of Rev3. Cryo-EM density for selected regions of Rev3 that highlight the differences in sequence with Pol3 (PDB ID: 3IAY), including residues in the inactive exonuclease domain, residues in close proximity to the CysBD, and the near absence of the β-hairpin region in Rev3. Also shown are close-up views of the coordination around the 4Fe-4S cluster, and the interfaces between the RIR and the palm and thumb domains.