The pentatricopeptide repeat (PPR) is a 35-

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

sequence motif In biology, a sequence motif is a nucleotide or amino-acid sequence pattern that is widespread and usually assumed to be related to biological function of the macromolecule. For example, an ''N''-glycosylation site motif can be defined as ''As ...

. Pentatricopeptide-repeat-containing proteins are a family of

proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

commonly found in the

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...

kingdom. They are distinguished by the presence of tandem degenerate PPR motifs and by the relative lack of introns in the genes coding for them. Approximately 450 such proteins have been identified in the

Arabidopsis ''Arabidopsis'' (rockcress) is a genus in the family Brassicaceae. They are small flowering plants related to cabbage and mustard. This genus is of great interest since it contains thale cress (''Arabidopsis thaliana''), one of the model organi ...

genome, and another 477 in the

rice Rice is the seed of the grass species ''Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima ''Oryza glaberrima'', commonly known as African rice, is one of the two domesticated rice species. It was first domesticated and grown i ...

genome. 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''. 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 A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...

and other

organelles In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the ...

and that they are possibly involved in

RNA editing RNA editing (also RNA modification) is a molecular process through which some cells can make discrete changes to specific nucleotide sequences within an RNA molecule after it has been generated by RNA polymerase. It occurs in all living organisms ...

. However many trans proteins are required for this editing to occur and research continues to look at which proteins are needed. 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 effector TAL (transcription activator-like) effectors (often referred to as TALEs, but not to be confused with the three amino acid loop extension homeobox class of proteins) are proteins secreted by some β- and γ-proteobacteria. Most of these are Xant ...

Examples

Human genes encoding proteins containing this repeat include: *

DENND4A C-myc promoter-binding protein is a protein that in humans is encoded by the ''DENND4A'' gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generati ...

, DENND4B, DENND4C * LRPPRC * PTCD1, PTCD2, PTCD3 * MRPS27

References

Amino acid motifs {{molecular-biology-stub