Features of the helicase region of RecQΔC. Features of the helicase region of RecQΔC. (A) View into the cleft formed by the two helicase subdomains. Color coding is the same as Figure 1A, except that helicase motifs are labeled and colored in grey, and residues corresponding to known BLM missense mutations are labeled and colored in orange. Sites where nucleotide and ssDNA have been observed to bind in other helicase structures are indicated. (B) Structure of ATPγS/Mn2+‐bound RecQΔC. (Inset) overlay of the apo‐ and ATPγS‐bound RecQΔC structures in yellow and grey, respectively. A slight relative rotation of the second helicase lobe is seen in the structure with bound nucleotide. (Main panel) Fo–Fc difference electron density (light blue) is contoured at 1.5 σ. Motif I is in an open conformation relative to its position in Figure 2A. The ATPγS (lavender) adenine moiety is sandwiched between Tyr23 and Arg27, and hydrogen bonds are formed between the N6 and N7 atoms of the adenine and the side chain of Gln30. The triphosphate is bound by interactions with Lys53 and backbone amides from motif I. A Mn2+ ion (cyan) is bound by Ser54 from motif I and Asp146 from motif II. Helicase motif labels and color‐coding are the same as in Figure 2A. Electron density was not observed for residues 296 to 299 (dashed line). Douglas A. Bernstein et al. EMBO J. 2003;22:4910-4921 © as stated in the article, figure or figure legend