Crystal structure of the Z alpha domain of the human editing enzyme ADAR1 bound to left-handed Z-DNA

The editing enzyme double-stranded RNA adenosine deaminase includes a DNA b inding domain, Z alpha, which is specific for Left-handed Z-DNA, The 2.1 an gstrom crystal structure of Z alpha complexed to DNA reveals that the subst rate is in the left-handed Z conformation. The contacts between Z alpha and Z-DNA are made primarily with the "zigzag" sugar-phosphate backbone, which provides a basis for the specificity for the Z conformation. A single base contact is observed to guanine in the syn conformation, characteristic of Z-DNA. Intriguingly, the helix-turn-helix motif, frequently used to recogni ze B-DNA, is used by Z alpha to contact Z-DNA.