A synthetic RNA editing factor edits its target site in chloroplasts and bacteria
Abstract Targeted cytidine to uridine RNA editing is a widespread phenomenon throughout the land plant lineage. Members of the pentatricopeptide repeat (PPR) protein family act as the specificity factors in this process. These proteins consist of helix-turn-helix domains, each of which recognises a single RNA nucleotide following a well-elucidated code. A cytidine deaminase-like domain (present at the C-terminus of some PPR editing factors or provided in trans via protein-protein interactions) is the catalytic domain in the process. The huge expansion of the PPR superfamily in land plants provides the sequence variation required for design of novel consensus-based RNA-binding proteins. We used this approach to construct a synthetic RNA editing factor designed to target one of the two sites in the Arabidopsis chloroplast transcriptome naturally recognised by the RNA editing factor CHLOROPLAST BIOGENESIS 19 (CLB19). We show that this designed editing factor specifically recognises the target sequence in in vitro binding assays and can partially complement a clb19 mutant. The designed factor is specific for the target rpoA site and does not recognise or edit the other site recognised by CLB19 in the clpP1 transcript. We show that the designed editing factor can function equally specifically in the bacterium E. coli, and shows some activity even in the absence of the editing cofactors that are often required for natural editing factor activity in plants. This study serves as a successful pilot into the design and application of programmable RNA editing factors based on plant PPR proteins.