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H3K36me
H3K36me is an epigenetic modification to the DNA packaging protein Histone H3, specifically, the mono-methylation at the 36th lysine residue of the histone H3 protein. There are diverse modifications at H3K36, such as phosphorylation, methylation, acetylation, and ubiquitylation, which have many important biological processes. The methylation of H3K36 has particularly had effects in transcriptional repression, alternative splicing, dosage compensation, DNA replication and repair, DNA methylation, and the transmission of the memory of gene expression from parents to offspring during development. Nomenclature H3K36me2 indicates dimethylation of lysine 36 on histone H3 protein subunit: Lysine methylation This diagram shows the progressive methylation of a lysine residue. The mono-methylation denotes the methylation present in H3K36me1. Lysine methylation is the addition of a methyl group to the lysine of histone proteins. This occurs via histone lysine methyltransferase (HMT ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Histones
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 are wrapped into 30-nanometer fibers that form tightly packed chromatin. Histones prevent DNA from becoming tangled and protect it from DNA damage. In addition, histones play important roles in gene regulation and DNA replication. Without histones, unwound DNA in chromosomes would be very long. For example, each human cell has about 1.8 meters of DNA if completely stretched out; however, when wound about histones, this length is reduced to about 90 micrometers (0.09 mm) of 30 nm diameter chromatin fibers. There are five families of histones which are designated H1/H5 (linker histones), H2, H3, and H4 (core histones). The nucleosome core is formed of two H2A-H2B dimers and a H3-H4 tetramer. The tight wrapping of DNA around histones ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Histone Code
The histone code is a hypothesis that the transcription of genetic information encoded in DNA is in part regulated by chemical modifications (known as ''histone marks'') to histone proteins, primarily on their unstructured ends. Together with similar modifications such as DNA methylation it is part of the epigenetic code. Histones associate with DNA to form nucleosomes, which themselves bundle to form chromatin fibers, which in turn make up the more familiar chromosome. Histones are globular proteins with a flexible N-terminus (taken to be the tail) that protrudes from the nucleosome. Many of the histone tail modifications correlate very well to chromatin structure and both histone modification state and chromatin structure correlate well to gene expression levels. The critical concept of the histone code hypothesis is that the histone modifications serve to recruit other proteins by specific recognition of the modified histone via protein domains specialized for such purposes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 and upregulation, downregulation of nearby genes via the formation of Heterochromatin, heterochromatic regions. Nomenclature H3K27me3 indicates Methylation, trimethylation of lysine 27 on histone H3 protein subunit: Lysine methylation This diagram shows the progressive methylation of a lysine residue. The tri-methylation denotes the methylation present in H3K27me3. Understanding histone modifications The genomic DNA of eukaryotic cells is wrapped around special protein molecules known as Histones. The complexes formed by the looping of the DNA are known as Chromatin. The basic structural unit of chromatin is the Nucleosome: this consists of the core octamer of histones (H2A, H2B, H3 and H4) as well as a linker histone and about 180 base pairs of DNA. Thes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
H3K4me3
H3K4me3 is an epigenetic modification to the DNA packaging protein Histone H3 that indicates tri-methylation at the 4th lysine residue of the histone H3 protein and is often involved in the regulation of gene expression. The name denotes the addition of three methyl groups ( trimethylation) to the lysine 4 on the histone H3 protein. H3 is used to package DNA in eukaryotic cells (including human cells), and modifications to the histone alter the accessibility of genes for transcription. H3K4me3 is commonly associated with the activation of transcription of nearby genes. H3K4 trimethylation regulates gene expression through chromatin remodeling by the NURF complex. This makes the DNA in the chromatin more accessible for transcription factors, allowing the genes to be transcribed and expressed in the cell. More specifically, H3K4me3 is found to positively regulate transcription by bringing histone acetylases and nucleosome remodelling enzymes (NURF). H3K4me3 also plays an impor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Histone Methyltransferase
Histone methyltransferases (HMT) are histone-modifying enzymes (e.g., histone-lysine N-methyltransferases and histone-arginine N-methyltransferases), that catalyze the transfer of one, two, or three methyl groups to lysine and arginine residues of histone proteins. The attachment of methyl groups occurs predominantly at specific lysine or arginine residues on histones H3 and H4. Two major types of histone methyltranferases exist, lysine-specific (which can be SET (Su(var)3-9, Enhancer of Zeste, Trithorax) domain containing or non-SET domain containing) and arginine-specific. In both types of histone methyltransferases, S-Adenosyl methionine (SAM) serves as a cofactor and methyl donor group. The genomic DNA of eukaryotes associates with histones to form chromatin. The level of chromatin compaction depends heavily on histone methylation and other post-translational modifications of histones. Histone methylation is a principal epigenetic modification of chromatin that determines ge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
H3K9me3
H3K9me3 is an epigenetic modification to the DNA packaging protein Histone H3. It is a mark that indicates the tri-methylation at the 9th lysine residue of the histone H3 protein and is often associated with heterochromatin. Nomenclature H3K9me3 indicates trimethylation of lysine 9 on histone H3 protein subunit: Lysine Methylation This diagram shows the progressive methylation of a lysine residue. The tri-methylation denotes the methylation present in H3K9me3 . Understanding histone modifications The genomic DNA of eukaryotic cells is wrapped around special protein molecules known as Histones. The complexes formed by the looping of the DNA are known as chromatin. The basic structural unit of chromatin is the nucleosome: this consists of the core octamer of histones (H2A, H2B, H3 and H4) as well as a linker histone and about 180 base pairs of DNA. These core histones are rich in lysine and arginine residues. The carboxyl (C) terminal end of these histones contribute to hi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
H3K4me1
H3K4me1 is an epigenetic modification to the DNA packaging protein Histone H3. It is a mark that indicates the mono-methylation at the 4th lysine residue of the histone H3 protein and often associated with gene enhancers. Nomenclature H3K4me1 indicates monomethylation of lysine 4 on histone H3 protein subunit: Lysine methylation This diagram shows the progressive methylation of a lysine residue. The mono-methylation denotes the methylation present in H3K4me1. Understanding histone modifications The genomic DNA of eukaryotic cells is wrapped around special protein molecules known as histones. The complexes formed by the looping of the DNA are known as chromatin. The basic structural unit of chromatin is the nucleosome: this consists of the core octamer of histones (H2A, H2B, H3 and H4) as well as a linker histone and about 180 base pairs of DNA. These core histones are rich in lysine and arginine residues. The carboxyl (C) terminal end of these histones contribute to his ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epigenetic
In biology, epigenetics is the study of stable phenotypic changes (known as ''marks'') that do not involve alterations in the DNA sequence. The Greek prefix '' epi-'' ( "over, outside of, around") in ''epigenetics'' implies features that are "on top of" or "in addition to" the traditional genetic basis for inheritance. Epigenetics most often involves changes that affect the regulation of gene expression, but the term can also be used to describe any heritable phenotypic change. Such effects on cellular and physiological phenotypic traits may result from external or environmental factors, or be part of normal development. The term also refers to the mechanism of changes: functionally relevant alterations to the genome that do not involve mutation of the nucleotide sequence. Examples of mechanisms that produce such changes are DNA methylation and histone modification, each of which alters how genes are expressed without altering the underlying DNA sequence. Gene expression can ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Methyllysine
Methyllysine is derivative of the amino acid residue lysine where the sidechain ammonium group has been methylated one or more times. Such methylated lysines play an important role in epigenetics; the methylation of specific lysines of certain histones in a nucleosome alters the binding of the surrounding DNA to those histones, which in turn affects the expression of genes on that DNA. The binding is affected because the effective radius of the positive charge is increased (methyl groups are larger than the hydrogen atoms they replace), reducing the strongest potential electrostatic attraction with the negatively charged DNA. It is thought that the methylation of lysine (and arginine) on histone tails does not directly affect their binding to DNA. Rather, such methyl marks recruit other proteins that modulate chromatin structure. In Protein Data Bank The Protein Data Bank (PDB) is a database for the three-dimensional structural data of large biological molecules, such as pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Histone Methylation
Histone methylation is a process by which methyl groups are transferred to amino acids of histone proteins that make up nucleosomes, which the DNA double helix wraps around to form chromosomes. Methylation of histones can either increase or decrease transcription of genes, depending on which amino acids in the histones are methylated, and how many methyl groups are attached. Methylation events that weaken chemical attractions between histone tails and DNA increase transcription because they enable the DNA to uncoil from nucleosomes so that transcription factor proteins and RNA polymerase can access the DNA. This process is critical for the regulation of gene expression that allows different cells to express different genes. Function Histone methylation, as a mechanism for modifying chromatin structure is associated with stimulation of neural pathways known to be important for formation of long-term memories and learning. Animal models have shown methylation and other epigenetic re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tn5 Transposon
A transposase is any of a class of enzymes capable of binding to the end of a transposon and catalysing its movement to another part of a genome, typically by a cut-and-paste mechanism or a replicative mechanism, in a process known as transposition. The word "transposase" was first coined by the individuals who cloned the enzyme required for transposition of the Tn3 transposon. The existence of transposons was postulated in the late 1940s by Barbara McClintock, who was studying the inheritance of maize, but the actual molecular basis for transposition was described by later groups. McClintock discovered that some segments of chromosomes changed their position, jumping between different loci or from one chromosome to another. The repositioning of these transposons (which coded for color) allowed other genes for pigment to be expressed. Transposition in maize causes changes in color; however, in other organisms, such as bacteria, it can cause antibiotic resistance. Transposition is al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleosome
A nucleosome is the basic structural unit of DNA packaging in eukaryotes. The structure of a nucleosome consists of a segment of DNA wound around eight histone proteins and resembles thread wrapped around a spool. The nucleosome is the fundamental subunit of chromatin. Each nucleosome is composed of a little less than two turns of DNA wrapped around a set of eight proteins called histones, which are known as a histone octamer. Each histone octamer is composed of two copies each of the histone proteins H2A, H2B, H3, and H4. DNA must be compacted into nucleosomes to fit within the cell nucleus. In addition to nucleosome wrapping, eukaryotic chromatin is further compacted by being folded into a series of more complex structures, eventually forming a chromosome. Each human cell contains about 30 million nucleosomes. Nucleosomes are thought to carry epigenetically inherited information in the form of covalent modifications of their core histones. Nucleosome positions in the gen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
