Representative conformations of nucleotide-binding pocket from all 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. Only residues with conformational changes are labeled in non-cognate systems for clarity. Dashed arrows for Gln440 in A:dCTP and A:dGTP system indicate a tendency of shifting, yet not significantly. Mg²⁺ (A), catalytic ion; Mg²⁺ (B), nucleotide-binding ion.