Pentatricopeptide repeat
The pentatricopeptide repeat (PPR) is a 35-amino acid sequence motif. Pentatricopeptide-repeat-containing proteins are a family of proteins commonly found in the plant kingdom. They are distinguished by the presence of tandem degenerate PPR motifs[1] and by the relative lack of introns in the genes coding for them.[2]
Approximately 450 such proteins have been identified in the Arabidopsis genome, and another 477 in the rice genome.[3] Despite the large size of the protein family, genetic data suggest that there is little or no redundancy of function between the PPR proteins in Arabidopsis.[2]
The purpose of PPR proteins is currently under dispute. It has been shown that a good deal of those in Arabidopsis interact (often essentially) with mitochondria and other organelles[2] and that they are possibly involved in RNA editing.[4] However many trans proteins are required for this editing to occur and research continues to look at which proteins are needed.[5]
The structure of the PPR has been resolved. It folds into a helix-turn-helix structure similar to those found in the tetratricopeptide repeat. Several repeats of the protein forms a ring around a single-strand RNA molecule in a sequence-sensitive way reminiscent of TAL effectors.[6]
Examples
Human genes encoding proteins containing this repeat include:
References
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