Figure 4.

Structure of TdT-μ chimera bound to a 1-nt-gapped DNA substrate with an incoming dNTP. A, single-nucleotide-gapped DNA substrate; upstream and downstream primers are represented in red and blue, respectively. The continuous template strand is depicted in cyan, and the incoming nucleotide is in gray. B, detailed view of the differences in the base moiety conformation in the ddCTP binary complex and in the gap-filling complex, accompanied by a change of rotamer in Arg⁴⁵⁴ and Arg⁴⁵⁸. C, overall structure of TdT-μ chimera in complex with a gap-filling DNA substrate. Loop1 (in blue) is not visible in electron density. The β2–α12 loop (junction) is indicated in gray dashed lines. D, DNA conformation in Pol μ gap-filling structure, for comparison (PDB entry 2IHM).