Central channel of the Polζ enzyme complex and conformational changes associated with DNA binding.A, central channel of Rev3 for DNA binding. Surfaces of the apo form and states A and B are shown in purple, cyan and green, respectively. The sizes of the channel openings were measured as 18.2 Å, 20.6 Å, and 20.7 Å for the apo form and states A and B, respectively. B, conformational changes of Rev3 loops (948–960 aa, 1050–1094 aa and 1095–1107 aa) upon DNA oligomer binding. The indicated loops of the apo form and DNA-bound Polζ are highlighted in purple and sea green, respectively. C, rotameric conformation of Rev3 K1214. The side chain of K1214 primary amine points toward the center of the hole in the apo form, whereas it moves away when the Polζ complex binds DNA. D, side chain of K1214 in DNA-bound Polζ. DNA backbone is colored yellow. The positively charged K1214 side chain points away from the negatively charged sugar-phosphate backbone.