Which enzyme class is commonly responsible for A-to-I RNA editing?

• A. DNA polymerases
• B. Adenosine deaminases acting on RNA (ADAR)
• C. Aminoacyl-tRNA synthetases
• D. Ribozymes

Answer: (B)

Adenosine-to-inosine RNA editing is carried out by enzymes known as adenosine deaminases acting on RNA. These ADAR enzymes remove an amino group from adenosine in RNA, converting it to inosine. Because inosine is read as guanosine by the cellular machinery during translation, splicing, and other RNA processes, this editing can change codons, splice sites, or microRNA interactions, leading to altered protein products or RNA behavior. ADARs typically act on double-stranded RNA regions and include enzymes like ADAR1 and ADAR2, which play major roles in many tissues, especially the brain. This mechanism is distinct from DNA-focused enzymes like DNA polymerases, from aminoacyl-tRNA synthetases, and from ribozymes, which are different kinds of RNA catalysts. Hence, the class responsible is adenosine deaminases acting on RNA.