Expression of heterologous ADAR enzymes in yeast indicates editing activity is affected by temperature, and identifies the mdADAR1 as a hyper transcriptome diversifier

RNA editing has become a focus of attention in many research fields. The most abundant form of RNA-editing in metazoans is A-to-I editing, mediated by the Adenosine Deaminase Acting on RNA (ADAR) enzymes, which binds dsRNAs. ADAR mediated A-to-I editing allows genomically-encoded nucleobases to be differently recognized, and is a powerful endogenous means of creating inner-transcriptome diversity. This makes it an attractive therapeutic tool. ADARs are present in all metazoa, but since genomes that express ADARs were subjected to selective pressures, it is challenging to differentiate the evolutionary effects and intrinsic substrate preference of them. Here we developed a novel approach that can be used to identify efficient enzymes using the yeast Saccharomyces cerevisiae, whose origin precedes the emergence ADARs and does not have the endogenous capacity of A-to-I editing.

Exogenically expressed ADARs had different effect on yeast viability and showed a diverse editing spectrum, demonstrating that the expression of heterologous ADARs in a selection-neutral environment can reveal their true editing potential. Since RNA secondary structure is affected by temperature, the enzymes most likely adapted distinctive mechanisms prompted among others by differences in body temperature, to better recognize their substrates. Using our yeast-based system, we show that temperature plays an important role in affecting RNA editing, and identified the mallard-duck ADAR1 as the most potent A-to-I RNA editor discovered so far. Elucidating such mechanisms could help to better understand ADARs evolution and serve as the framework for more effective designs to better redirect exogenous ADARs and to restrain their activity.