InterPro: IPR002885 Pentatricopeptide repeat

This entry represents the PPR repeat.

Pentatricopeptide repeat (PPR) proteins are characterised by tandem repeats of a degenerate 35 amino acid motif [1]. Most of PPR proteins have roles in mitochondria or plastid [2]. PPR repeats were discovered while screening Arabidopsis proteins for those predicted to be targeted to mitochondria or chloroplast [1, 3]. Some of these proteins have been shown to play a role in post-transcriptional processes within organelles and they are thought to be sequence-specific RNA-binding proteins [4, 5, 6]. Plant genomes have between one hundred to five hundred PPR genes per genome whereas non-plant genomes encode two to six PPR proteins.

Although no PPR structures are yet known, the motif is predicted to fold into a helix-turn-helix structure similar to those found in the tetratricopeptide repeat (TPR) family (see PDOC50005) [1].

The plant PPR protein family has been divided in two subfamilies on the basis of their motif content and organisation [3, 7].

Examples of PPR repeat-containing proteins include PET309 P32522, which may be involved in RNA stabilisation [8], and crp1, which is involved in RNA processing [9]. The repeat is associated with a predicted plant protein O49549 that has a domain organisation similar to the human BRCA1 protein.