Abstract
RNA-editing by adenosine deaminases acting on RNA (ADARs) converts adenosines to inosines in structured RNAs. Inosines are read as guanosines by most cellular machineries. A to I editing has two major functions: first, marking endogenous RNAs as “self”, therefore helping the innate immune system to distinguish repeat- and endogenous retrovirus-derived RNAs from invading pathogenic RNAs; and second, recoding the information of the coding RNAs, leading to the translation of proteins that differ from their genomically encoded versions. It is obvious that these two important biological functions of ADARs will differ during development, in different tissues, upon altered physiological conditions or after exposure to pathogens. Indeed, different levels of ADAR-mediated editing have been observed in different tissues, as a response to altered physiology or upon pathogen exposure. In this review, we describe the dynamics of A to I editing and summarize the known and likely mechanisms that will lead to global but also substrate-specific regulation of A to I editing.
Highlights
ADARsAdenosine deaminases acting on RNA (ADARs)Adenosine deaminases acting on RNA (ADARs) convert adenosines to inosines in structured and double-stranded RNAs (Figure 1)
Evolutionary, ADARs are related to Adenosine Deaminases Acting on tRNAs (ADATs), which are tRNA deaminating enzymes that are responsible for the introduction of inosines at the wobble position of certain tRNAs [2]
One of the first post-translational modifications found on ADAR proteins was the SUMOylation of ADAR1 [37]
Summary
Adenosine deaminases acting on RNA (ADARs) convert adenosines to inosines in structured and double-stranded RNAs (Figure 1). Evolutionary, ADARs are related to Adenosine Deaminases Acting on tRNAs (ADATs), which are tRNA deaminating enzymes that are responsible for the introduction of inosines at the wobble position of certain tRNAs [2]. ADARs acquired double-stranded RNAbinding domains that allow them to bind to their substrate RNAs [3]. Depending on the organismic group, different types of ADARs exist that all harbor the deaminase domain at their C-terminal ends but contain a variable number of RNA-binding motifs (Figure 1). Three ADAR family members can be found. The most obvious differences between these three family members are seen in the number of double-stranded RNAbinding domains and in the amino-terminal extensions of the ADAR enzymes. In the aminoterminal regions of the ADARs, additional nucleic acid-binding domains and regions controlling intracellular localization of the harboring enzymes can be found (Figure 1)
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