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Figure 4
Possible carboxylate–hydroxyl relay mechanism including His124. (a) Schematic drawing of the proposed His124-dependent proton-relay pathway. The amino-acid residues, Mg2+ ions and H2Oδ water molecule are drawn based on the current crystal structure. A substrate is drawn on the basis of the hypothetical structure in comparison with the human RNase H1–RNA/DNA hybrid complex (PDB entry 2qkk). A putative nucleophilic attack water (gray) is also indicated. (b) A putative mechanism for the formation of an intermediate ternary complex after the RNase HI–Zn2+ complex. The Zn2+-coordinated water molecule resembling that in RNH_Zn_1 and RNH_Zn_2 is indicated in the first step of the scheme.

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ISSN: 2059-7983
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