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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 reinforcing the DNA during cell division, preventing DNA damage, and regulating gene expression and DNA replication. During mitosis and meiosis, chromatin facilitates proper segregation of the chromosomes in anaphase; the characteristic shapes of chromosomes visible during this stage are the result of DNA being coiled into highly condensed chromatin.
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.
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.
A nuclear localization signalorsequence (NLS) is an amino acid sequence that 'tags' a protein for import into the cell nucleus by nuclear transport. Typically, this signal consists of one or more short sequences of positively charged lysines or arginines exposed on the protein surface. Different nuclear localized proteins may share the same NLS. An NLS has the opposite function of a nuclear export signal (NES), which targets proteins out of the nucleus.
An orphon is a gene located outside the main chromosomal locus, i.e., it may be dispersed to an unconnected genomic location.
Histone H1 is one of the five main histone protein families which are components of chromatin in eukaryotic cells. Though highly conserved, it is nevertheless the most variable histone in sequence across species.
Chromatin remodeling is the dynamic modification of chromatin architecture to allow access of condensed genomic DNA to the regulatory transcription machinery proteins, and thereby control gene expression. Such remodeling is principally carried out by 1) covalent histone modifications by specific enzymes, e.g., histone acetyltransferases (HATs), deacetylases, methyltransferases, and kinases, and 2) ATP-dependent chromatin remodeling complexes which either move, eject or restructure nucleosomes. Besides actively regulating gene expression, dynamic remodeling of chromatin imparts an epigenetic regulatory role in several key biological processes, egg cells DNA replication and repair; apoptosis; chromosome segregation as well as development and pluripotency. Aberrations in chromatin remodeling proteins are found to be associated with human diseases, including cancer. Targeting chromatin remodeling pathways is currently evolving as a major therapeutic strategy in the treatment of several cancers.
Nucleophosmin (NPM), also known as nucleolar phosphoprotein B23 or numatrin, is a protein that in humans is encoded by the NPM1 gene.
Paired amphipathic helix protein Sin3a is a protein that in humans is encoded by the SIN3A gene.
In enzymology, a nucleoplasmin ATPase (EC 3.6.4.11) is an enzyme that catalyzes the chemical reaction
Chromatin assembly factor 1 subunit B is a protein that in humans is encoded by the CHAF1B gene.
Histone chaperone ASF1A is a protein that in humans is encoded by the ASF1A gene.
Nucleoplasmin-3 is a protein that in humans is encoded by the NPM3 gene.
Chromatin immunoprecipitation (ChIP) is a type of immunoprecipitation experimental technique used to investigate the interaction between proteins and DNA in the cell. It aims to determine whether specific proteins are associated with specific genomic regions, such as transcription factors on promoters or other DNA binding sites, and possibly define cistromes. ChIP also aims to determine the specific location in the genome that various histone modifications are associated with, indicating the target of the histone modifiers. ChIP is crucial for the advancements in the field of epigenomics and learning more about epigenetic phenomena.
In the field of molecular biology, the Mi-2/NuRDcomplex, is a group of associated proteins with both ATP-dependent chromatin remodeling and histone deacetylase activities. As of 2007, Mi-2/NuRD was the only known protein complex that couples chromatin remodeling ATPase and chromatin deacetylation enzymatic functions.
William Charles Earnshaw is Professor of Chromosome Dynamics at the University of Edinburgh where he has been a Wellcome Trust Principal Research Fellow since 1996.
Chromatin assembly factor-1 (CAF-1) is a protein complex — including Chaf1a (p150), Chaf1b (p60), and p48 subunits in humans, or Cac1, Cac2, and Cac3, respectively, in yeast— that assembles histone tetramers onto replicating DNA during the S phase of the cell cycle.
In molecular biology, the linker histone H1 is a protein family forming a critical component of eukaryotic chromatin. H1 histones bind to the linker DNA exiting from the nucleosome core particle, while the core histones form the octamer core of the nucleosome around which the DNA is wrapped.
Colin Dingwall is a British biochemist and cell biologist. He is a Fellow of the Royal Society of Biology and a Life Member of Clare Hall, Cambridge UK. Working with Ron Laskey and Sir John Gurdon he established the identified the bipartite nuclear localization sequence which is the major signal for protein entry into the nucleus.
Xenopus egg extract is a lysate that is prepared by crushing the eggs of the African clawed frog Xenopus laevis. It offers a powerful cell-free system for studying various cell biological processes, including cell cycle progression, nuclear transport, DNA replication and chromosome segregation. It is also called Xenopus egg cell-free system or Xenopus egg cell-free extract.
References
- ↑ Dingwall C, Laskey RA (February 1990). "Nucleoplasmin: the archetypal molecular chaperone". Seminars in Cell Biology. 1 (1): 11–17. PMID 1983266.
- 1 2 Rice P, Garduño R, Itoh T, Katagiri C, Ausio J (June 1995). "Nucleoplasmin-mediated decondensation of Mytilus sperm chromatin. Identification and partial characterization of a nucleoplasmin-like protein with sperm-nuclei decondensing activity in Mytilus californianus". Biochemistry. 34 (23): 7563–7568. doi:10.1021/bi00023a001. PMID 7779801.
- ↑ Dingwall C, Sharnick SV, Laskey RA (September 1982). "A polypeptide domain that specifies migration of nucleoplasmin into the nucleus". Cell. 30 (2): 449–458. doi:10.1016/0092-8674(82)90242-2. PMID 6814762.
- 1 2 Tejun S, Yaozhou Z (2007). "Nucleoplasmin, an Important Nuclear Chaperone". Chinese Journal of Biochemistry and Molecular Biology. 23 (9): 718–723.
- ↑ Frehlick LJ, Eirín-López JM, Ausió J (January 2007). "New insights into the nucleophosmin/nucleoplasmin family of nuclear chaperones". BioEssays. 29 (1): 49–59. doi:10.1002/bies.20512. PMID 17187372.
- ↑ "Nucleoplasmin-like core domain superfamily". Superfamily 1.75, HMM Library and Genome Assignment Server.
- ↑ Ramos I, Fernández-Rivero N, Arranz R, Aloria K, Finn R, Arizmendi JM, et al. (January 2014). "The intrinsically disordered distal face of nucleoplasmin recognizes distinct oligomerization states of histones". Nucleic Acids Research. 42 (2): 1311–1325. doi:10.1093/nar/gkt899. PMC 3902905 . PMID 24121686.
- ↑ "Nucleoplasmin family". InterPro. EMBL-EBI, Wellcome Trust Genome Campus,European Molecular Biology Laboratory.
