5KFA: Human Dna Polymerase Eta-Dna Ternary Complex: Ground State A (K+ Mes) With 1 Ca2+ Ion
reference: Capture of a third Mg(2)(+) is essential for catalyzing DNA synthesis., Gao Y, Yang W, Science. 2016 Jun 10;352(6291):1334-7. doi: 10.1126/science.aad9633. PMID: 27284197

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).