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Z-Z DNA junction. Molecular model of a junction between two left-handed DNA double helices (Z DNA, down centre) stabilised by the Z alpha domain of the human RNA-editing enzyme ADAR1 (double-stranded RNA adenosine deaminase, right and left). ADAR1 de-stabilises double stranded RNA (ribonucleic acid) by converting adenosine to inosine in the genetic sequence. ADAR1 is needed for the breakdown of adenosine from food and for the turnover of nucleic acids (RNA and DNA) in tissues. (KEYSTONE/SCIENCE PHOTO LIBRARY/LAGUNA DESIGN/SCIENCE PHOTO LIBRARY)