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Published in final edited form as: Wiley Interdiscip Rev RNA. 2015 Nov 2;7(1):33–51. doi: 10.1002/wrna.1313

A) Pre-edited mRNAs are transcribed from mitochondrial maxicircles, while the majority of gRNAs are transcribed from the minicircle component of mitochondrial DNA. The gRNA 5’ anchor region (olive) basepairs with the mRNA and the gRNA information region (yellow) directs the number of U's inserted or deleted. The gRNA 3’ oligo(U) tail stabilizes the gRNA/mRNA interaction. Enzymes contained within the RNA editing core complex (RECC) catalyze mRNA endonucleolytic cleavage at an editing sites, U insertion by a 3’ TUTase, and U deletion by a U-specific exoribonuclease as directed by the sequences of gRNAs. Cleaved mRNAs are resealed by RNA ligases. B) Multi-round editing entails sequential utilization of multiple gRNAs. Because the anchor region of a given gRNA basepairs with edited mRNA sequence specified by the prior gRNA, editing progresses in a 3’ to 5’ direction along an mRNA. Multiple black arrowheads symbolize multiple editing sites within an editing block, as defined by the hybridized gRNA. Dashed gRNA labels indicate that they are turned over during/after an editing block has been processed. An editing domain is a stretch of mRNA sequence that requires the gRNA cascade for its processing.

A) Pre-edited mRNAs are transcribed from mitochondrial maxicircles, while the majority of gRNAs are transcribed from the minicircle component of mitochondrial DNA. The gRNA 5’ anchor region (olive) basepairs with the mRNA and the gRNA information region (yellow) directs the number of U's inserted or deleted. The gRNA 3’ oligo(U) tail stabilizes the gRNA/mRNA interaction. Enzymes contained within the RNA editing core complex (RECC) catalyze mRNA endonucleolytic cleavage at an editing sites, U insertion by a 3’ TUTase, and U deletion by a U-specific exoribonuclease as directed by the sequences of gRNAs. Cleaved mRNAs are resealed by RNA ligases. B) Multi-round editing entails sequential utilization of multiple gRNAs. Because the anchor region of a given gRNA basepairs with edited mRNA sequence specified by the prior gRNA, editing progresses in a 3’ to 5’ direction along an mRNA. Multiple black arrowheads symbolize multiple editing sites within an editing block, as defined by the hybridized gRNA. Dashed gRNA labels indicate that they are turned over during/after an editing block has been processed. An editing domain is a stretch of mRNA sequence that requires the gRNA cascade for its processing.