PPR

Yagi Y, Hayashi S, Kobayashi K, Hirayama T & Nakamura T 2013 Elucidation of the RNA recognition code for pentatricopeptide repeat proteins involved in organelle RNA editing in plants. PLoS ONE 8:e57286.

• the PPR tract recognized the upstream nucleotide sequence by a 1-motif to 1-nucleotide correspondence, with no gap sequence, in contrast to the classical P-type PPR protein involved in processes other than RNA editing, e.g., PPR10, CRP1, and HCF152, which contain gaps in the PPR/RNA duplex

• the editing PPR protein contains an additional C-terminal motif (E, E+, and DYW)
• the E motif is predicted to contain 4 repetitions of α helices, corresponding to those of 2 PPR motifs
• the additional motif(s), as well as an as-of-yet undefined editing enzyme, may be involved in the recognition of nucleotides in the vicinity of the editable C residues
• it is also possible that the recently identified novel protein family of multiple organellar RNA editing factor (MORF, also known as RNA-editing factor interacting protein [RIP]) is involved in sequence recognition for RNA editing
• this may also explain our imperfect computational assignments for the target RNAs