Stunning Intricacies of RNA Editing Complexes RECC, RESC, and REH2C: Functional Organization, Developmental Regulation, and Evolutionary History in Kinetoplastid Protists

Abstract

RNA metabolism in kinetoplastid protists (Kinetoplastea), including trypanosomes and Leishmania, involves unique post-transcriptional mitochondrial RNA editing that creates translatable mRNAs through uridine (U) insertions and deletions (U-indels) directed by antisense guide RNAs (gRNAs). Like other biological processes that require specific RNA targeting, this system faces several challenges beyond coordinating its many components: assembling mRNA-gRNA hybrids, recognizing hundreds of sites, and accurately distinguishing pre-edited, partially edited, and fully edited transcripts in the mitochondrial environment. In parasites such as Trypanosoma brucei, significant energetic adaptations to different host environments also involve critical editing changes during development. The editing holoenzyme includes three molecular complexes and isoforms that carry most proteins: RNA Editing Catalytic Complexes (RECCs), which catalyze U-indel cycles; RNA Editing Substrate Complexes (RESCs), which serve as scaffolds to coordinate the editing components; and the RNA Editing Helicase 2 Complex (REH2C), which contains key proteins involved in developmental editing regulation. However, more proteins and functions are being discovered. The editing system, best understood in T. brucei, shows considerable evolutionary conservation in its core machinery; however, it varies in the extent of RNA editing and the organization of mitochondrial mRNA and gRNA genes across different species. Here we explore recent progress in our understanding of RNA editing and the growing use of modern computational tools, including artificial intelligence (AI) and structural methods, to examine function, organization, developmental regulation, and evolutionary aspects of this amazing system. This article is categorized under: RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes RNA Processing > RNA Editing and Modification.

Keywords: RECC; REH2C; RESC; RNA editing; developmental regulation; editing complexes; kinetoplastids.