Nucleic Acid Editing by Adenosine Deaminase Enzymes

RNA editing is crucial to the genetic diversity and structural complexity of organisms. ADAR (adenosine deaminase acting on RNA) is an RNA editing enzyme that creates a mutation of adenosine to inosine. The human ADAR2 (hADAR2) enzyme is known to edit RNA; however, it contains minor sequence homology with the cytidine deaminase enzymes, APOBEC and AID, which are known to edit both DNA and RNA (11 & 12). The ability of hADAR2 to edit DNA was tested through transformation into the Saccharomyces cerevisiae yeast strain BY4741. DNA editing was tested by determining if the transformed yeast became resistant to the antibiotic canavanine. Another editing enzyme within the ADAR classification is adenosine deaminase that acts on tRNA (ADAT). The structure of the ADAT1 from the organism, Candida albicans, will be determined through x-ray crystallography. The plasmid expressing the caADAT enzyme was purified from E. coli. The plasmid was then transformed into the Saccharomyces cerevisiae strain BCY123. Expression of the ADAT gene was activated in yeast using the GAL promoter system. caADAT protein is histone-tagged and was purified using a nickel column. The crystals of the caADAT protein will be grown and diffracted to determine the structure