Pentatricopeptide Repeat Protein
Encyclopedia
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 and by the relative lack of introns in the genes coding for them.
Approximately 450 such proteins have been identified in the arabidopsis
genome, and another 477 in the rice
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 and other organelles and that they are possibly involved in RNA editing
. 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 not yet been determined, the motif is predicted to fold into a helix-turn-helix
structure similar to those found in the tetratricopeptide
repeat.
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
sequence motif
Sequence motif
In genetics, a sequence motif is a nucleotide or amino-acid sequence pattern that is widespread and has, or is conjectured to have, a biological significance...
. Pentatricopeptide repeat containing proteins are a family of proteins commonly found in the plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
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 thaliana
Arabidopsis thaliana is a small flowering plant native to Europe, Asia, and northwestern Africa. A spring annual with a relatively short life cycle, arabidopsis is popular as a model organism in plant biology and genetics...
genome, and another 477 in the rice
Rice
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...
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
Arabidopsis thaliana
Arabidopsis thaliana is a small flowering plant native to Europe, Asia, and northwestern Africa. A spring annual with a relatively short life cycle, arabidopsis is popular as a model organism in plant biology and genetics...
.
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 and that they are possibly involved in RNA editing
RNA editing
The term RNA editing describes those molecular processes in which the information content in an RNA molecule is altered through a chemical change in the base makeup. To date, such changes have been observed in tRNA, rRNA, mRNA and microRNA molecules of eukaryotes but not prokaryotes...
. 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 not yet been determined, the motif is predicted to fold into a helix-turn-helix
Helix-turn-helix
In proteins, the helix-turn-helix is a major structural motif capable of binding DNA. It is composed of two α helices joined by a short strand of amino acids and is found in many proteins that regulate gene expression...
structure similar to those found in the tetratricopeptide
Tetratricopeptide
The tetratricopeptide repeat is a structural motif. It consists in a degenerate 34 amino acid sequence motif identified in a wide variety of proteins. It is found in tandem arrays of 3–16 motifs, which form scaffolds to mediate protein–protein interactions and often the assembly of multiprotein...
repeat.
Examples
Human genes encoding proteins containing this repeat include:- DENND4ADENND4AC-myc promoter-binding protein is a protein that in humans is encoded by the DENND4A gene.-Further reading:...
, DENND4B, DENND4C - LRPPRCLRPPRCLeucine-rich PPR motif-containing protein, mitochondrial is a protein that in humans is encoded by the LRPPRC gene. Transcripts ranging in size from 4.8 to 7.0 kb which result from alternative polyadenylation have been reported for this gene.-Function:...
- PTCD1, PTCD2, PTCD3