PRC2 (polycomb repressive complex 2) is one of the two classes of

polycomb-group proteins Polycomb-group proteins (PcG proteins) are a family of protein complexes first discovered in fruit flies that can remodel chromatin such that epigenetic silencing of genes takes place. Polycomb-group proteins are well known for silencing Hox genes ...

or (PcG). The other component of this group of proteins is PRC1 (

Polycomb Repressive Complex 1 Polycomb repressive complex 1 (PRC1) is one of the two classes of Polycomb Repressive complexes, the other being PRC2. Polycomb-group proteins play a major role in transcriptional regulation during development. Polycomb Repressive Complexes PRC1 an ...

). This complex has

histone In biology, histones are highly basic proteins abundant in lysine and arginine residues that are found in eukaryotic cell nuclei. They act as spools around which DNA winds to create structural units called nucleosomes. Nucleosomes in turn a ...

methyltransferase Methyltransferases are a large group of enzymes that all methylate their substrates but can be split into several subclasses based on their structural features. The most common class of methyltransferases is class I, all of which contain a Ross ...

activity and primarily methylates

histone H3 Histone H3 is one of the five main histones involved in the structure of chromatin in eukaryotic cells. Featuring a main globular domain and a long N-terminal tail, H3 is involved with the structure of the nucleosomes of the 'beads on a stri ...

on lysine 27 (i.e.

H3K27me3 H3K27me3 is an epigenetic modification to the DNA packaging protein Histone H3. It is a mark that indicates the tri-methylation of lysine 27 on histone H3 protein. This tri-methylation is associated with the downregulation of nearby genes via t ...

), a mark of transcriptionally silent

chromatin Chromatin is a complex of DNA and protein found in eukaryotic cells. The primary function is to package long DNA molecules into more compact, denser structures. This prevents the strands from becoming tangled and also plays important roles in r ...

. PRC2 is required for initial targeting of genomic region (PRC Response Elements or PRE) to be silenced, while PRC1 is required for stabilizing this silencing and underlies cellular memory of silenced region after

cellular differentiation Cellular differentiation is the process in which a stem cell alters from one type to a differentiated one. Usually, the cell changes to a more specialized type. Differentiation happens multiple times during the development of a multicellular ...

. PRC1 also mono-ubiquitinates

histone H2A Histone H2A is one of the five main histone proteins involved in the structure of chromatin in eukaryotic cells. The other histone proteins are: H1, H2B, H3 and H4. Background Histones are proteins that package DNA into nucleosomes. Hist ...

on lysine 119 (H2AK119Ub1). These

protein 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 ...

s are required for long term epigenetic silencing of chromatin and have an important role in

stem cell In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type o ...

differentiation and early

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

nic development. PRC2 are present in most

multicellular organism A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- ...

s. The mouse PRC2 has four subunits:

Suz12 Polycomb protein SUZ12 is a protein that in humans is encoded by the ''SUZ12'' gene. Function This zinc finger gene has been identified at the breakpoints of a recurrent chromosomal translocation reported in endometrial stromal sarcoma. Recomb ...

(

zinc finger A zinc finger is a small protein structural motif that is characterized by the coordination of one or more zinc ions (Zn2+) in order to stabilize the fold. It was originally coined to describe the finger-like appearance of a hypothesized struct ...

), Eed,

Ezh1 #REDIRECT EZH1 {{R from other capitalization ...

Ezh2 Enhancer of zeste homolog 2 (EZH2) is a histone-lysine N-methyltransferase enzyme ( EC 2.1.1.43) encoded by gene, that participates in histone methylation and, ultimately, transcriptional repression. EZH2 catalyzes the addition of methyl groups ...

(

SET domain Set, The Set, SET or SETS may refer to: Science, technology, and mathematics Mathematics *Set (mathematics), a collection of elements * Category of sets, the category whose objects and morphisms are sets and total functions, respectively Electr ...

with histone methyltransferase activity) and

Rbbp4 #REDIRECT RBBP4 {{R from other capitalization ...

(histone

binding domain In molecular biology, binding domain is a protein domain which binds to a specific atom or molecule, such as calcium or DNA. A protein domain is a part of a protein sequence and a tertiary structure that can change or evolve, function, and liv ...

). PRC2 can bind to H3K27me3 and repress neighboring nucleosomes, thus spreading the repression. PRC2 has a role in

X chromosome inactivation X-inactivation (also called Lyonization, after English geneticist Mary Lyon) is a process by which one of the copies of the X chromosome is inactivated in therian female mammals. The inactive X chromosome is silenced by being packaged into a ...

, in maintenance of stem cell fate,Heurtier, V., Owens, N., Gonzalez, I. et al. The molecular logic of Nanog-induced self-renewal in mouse embryonic stem cells. Nat Commun 10, 1109 (2019). https://doi.org/10.1038/s41467-019-09041-z and in imprinting. Aberrant expression of PRC2 has been observed in

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

. Both loss and gain-of-function mutations in PRC2 components have been identified in various human

cancers Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...

, suggesting complex roles of these components in malignancy. Polycomb group genes directly and indirectly regulate the

DNA damage DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA d ...

response which acts as an anti-cancer barrier. The PRC2 complex appears to be present at sites of DNA double-strand breaks where it promotes repair of such breaks by

non-homologous end joining Non-homologous end joining (NHEJ) is a pathway that repairs double-strand breaks in DNA. NHEJ is referred to as "non-homologous" because the break ends are directly ligated without the need for a homologous template, in contrast to homology direc ...

. The PRC2 is

evolutionarily conserved In evolutionary biology, conserved sequences are identical or similar sequences in nucleic acids ( DNA and RNA) or proteins across species ( orthologous sequences), or within a genome ( paralogous sequences), or between donor and receptor tax ...

, and has been found in mammals, insects, fungi, and plants.

In plants

In '' Arabidopsis thaliana'', a plant model organism, several variants of the core subunits have been identified.

Homologs A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization. Homologs have the same genes in the same loci where they provide points alon ...

of the Suz12 subunit are: Embryonic flower 2 (EMF2), reduced vernalization response 2 (VRN2), fertilization independent seed 2 (FIS2). There is one Eed homolog, fertilization independent endosperm (FIE). three Ezh1/Ezh2 homologs, curly leaf (CLF), swinger (SWN), medea (MEA), and one Rbbp4 homolog, multicopy suppressor of IRA1 (MSI1). Many other accessory components of PRC2 complex in Arabidopsis have been identifi

References

{{reflist Proteins Articles containing video clips ru:Белки группы polycomb

In plants

See also

References