Representative active site arrangements from all pol μ cognate and non-cognate systems.

(A) A:dTTP cognate system; (B) A:dCTP non-cognate system; (C) A:dATP non-cognate system; (D) A(syn):dATP non-cognate system; (E) A:dGTP non-cognate system; (F) A(syn):dGTP non-cognate system; (G) T:dATP cognate system; (H) T:dCTP non-cognate system; (I) T:dGTP non-cognate system. The two cognate systems (A and G) are labeled in yellow. Systems with significantly distorted active site compared to cognate A:dTTP system are titled in red. Flipped His329 in A:dATP and A:dCTP systems are marked as red. Bold dashed lines indicate coordination around Mg²⁺; thin dashed lines indicate hydrogen bonds. Mg²⁺ (A), catalytic ion; Mg²⁺ (B), nucleotide-binding ion.