Figure 1. RNA editing core complex (RECC).

(A) Basic reaction steps at each editing site include gRNA-directed cleavage of the mRNA, followed by either a 3′-U exonuclease or a 3′ TUTase acting on the 3’-end of the cleaved upstream fragment, then resealing of the mRNA by RNA ligase. The gRNA-directed cleavage reactions at U-deletional and U-insertional editing sites require distinct endonucleases with different cleavage reaction mechanisms: the former requires an adenylate nucleotide (+), while the latter is inhibited by adenylates (−). (B) Editing by multiple gRNAs. The initiating gRNA (gRNA-1) and subsequent gRNAs (gRNA-2…gRNA-n) are depicted with pre-edited, partially edited, and fully edited mRNA. After a full block of editing is completed (depicted by a continuous duplex) the responsible gRNA is replaced by the next upstream gRNA. The exiting gRNA is thought to be degraded by a putative “discard” pathway (depicted by a broken line). (C) Variants of the RECC with shared proteins and alternative endonuclease modules for insertion and deletion editing. Note that B9 and B10 are not canonical RESC proteins because they are not regularly observed in the purifications of RECC. B9 and B10 may be only found in a subset of complexes and are depicted in a box to distinguish them from canonical RECC proteins. BS3 crosslinks between RNase III (RIII)-like proteins are indicated with lines. (D) Summary of the combinatorial potential of RIII-like proteins based on the BS3 crosslinking data in panel C. Additional potential interactions between RIII-like proteins including X1 and A-proteins are included.