Ribonuclease III-like domain of Ribonuclease III-like domain of RNA-editing catalytic complex (RECC) protein KREPB5
KREPB5 (MP44) has a divergent RNase III domain and is a component of the RNA-editing catalytic complex (RECC) involved in U-insertion/deletion mRNA editing during kinetoplast RNA processing. The mitochondrial DNA of Trypanosomatids, known as the kinetoplast DNA (kDNA or mtDNA), consists of a network of dozens of maxicircles and thousands of minicircles concatenated together. Maxicircles are equivalent to other eukaryotic mitochondrial DNAs, while minicircles encode guide RNAs (gRNAs) involved in U-insertion/deletion editing processes exclusive of Trypanosomatids that produce the maturation of the maxicircle-encoded transcripts. Although most gRNAs are encoded by minicircles, varying numbers of maxicircle-encoded gRNAs have been identified in kinetoplastids species. Trypanosoma brucei maxicircles encode 9S and 12S rRNAs, two gRNAs, two ribosomal proteins and 16 subunits of respiratory complexes. 12 of the 18 maxicircle genes are present as cryptogenes whose transcripts require U-insertion/deletion editing, mediated by gRNAs, to restore a protein-coding capacity. The RECC core complex comprises a U-insertion subcomplex (KRET2 TUTase, KREPA1 zinc-finger protein, and KREL2 RNA ligase), a U-deletion subcomplex (KREX2 exonuclease, KREPA2 zinc-finger protein, and KREL1 RNA ligase), and six structural and/or RNA-binding proteins (KREPA3, KREPA4, KREPA5, KREPA6, KREPB4, and KREPB5). This core complex interacts with one of three RNase III family endonucleases (KREN1, KREN2, and KREN3) that may partner with one or more partner protein(s) with divergent RNase III domains, such as KREN1/KREPB8, KREN2/KREPB7, KREN3/KREPB6. KREPB4-KREPB10 have divergent RNase III domains. RECC interacts with two other complexes, the RNA-editing helicase 2 complex (REH2C) and the RNA-editing substrate-binding complex (RESC) to form an assembly (editosome/holoenzyme) that carries out U-insertion/deletion mRNA editing. The C2H2 zinc finger that is present in related KREB proteins is not conserved in this subfamily.
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