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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.
Histone acetyltransferases (HATs) are enzymes that acetylate conserved lysine amino acids on histone proteins by transferring an acetyl group from acetyl-CoA to form ε-N-acetyllysine. DNA is wrapped around histones,and,by transferring an acetyl group to the histones,genes can be turned on and off. In general,histone acetylation increases gene expression.
In molecular biology,a histone octamer is the eight-protein complex found at the center of a nucleosome core particle. It consists of two copies of each of the four core histone proteins. The octamer assembles when a tetramer,containing two copies of H3 and two of H4,complexes with two H2A/H2B dimers. Each histone has both an N-terminal tail and a C-terminal histone-fold. Each of these key components interacts with DNA in its own way through a series of weak interactions,including hydrogen bonds and salt bridges. These interactions keep the DNA and the histone octamer loosely associated,and ultimately allow the two to re-position or to separate entirely.
DNA-binding proteins are proteins that have DNA-binding domains and thus have a specific or general affinity for single- or double-stranded DNA. Sequence-specific DNA-binding proteins generally interact with the major groove of B-DNA,because it exposes more functional groups that identify a base pair.
HMGN proteins are members of the broader class of high mobility group (HMG) chromosomal proteins that are involved in regulation of transcription,replication,recombination,and DNA repair.
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.
Histone H4 is one of the five main histone proteins involved in the structure of chromatin in eukaryotic cells. Featuring a main globular domain and a long N-terminal tail,H4 is involved with the structure of the nucleosome of the 'beads on a string' organization. Histone proteins are highly post-translationally modified. Covalently bonded modifications include acetylation and methylation of the N-terminal tails. These modifications may alter expression of genes located on DNA associated with its parent histone octamer. Histone H4 is an important protein in the structure and function of chromatin,where its sequence variants and variable modification states are thought to play a role in the dynamic and long term regulation of genes.
Histone H2A is one of the five main histone proteins involved in the structure of chromatin in eukaryotic cells.
High-Mobility Group or HMG is a group of chromosomal proteins that are involved in the regulation of DNA-dependent processes such as transcription,replication,recombination,and DNA repair.
The family of heterochromatin protein 1 (HP1) consists of highly conserved proteins,which have important functions in the cell nucleus. These functions include gene repression by heterochromatin formation,transcriptional activation,regulation of binding of cohesion complexes to centromeres,sequestration of genes to the nuclear periphery,transcriptional arrest,maintenance of heterochromatin integrity,gene repression at the single nucleosome level,gene repression by heterochromatization of euchromatin,and DNA repair. HP1 proteins are fundamental units of heterochromatin packaging that are enriched at the centromeres and telomeres of nearly all eukaryotic chromosomes with the notable exception of budding yeast,in which a yeast-specific silencing complex of SIR proteins serve a similar function. Members of the HP1 family are characterized by an N-terminal chromodomain and a C-terminal chromoshadow domain,separated by a hinge region. HP1 is also found at some euchromatic sites,where its binding can correlate with either gene repression or gene activation. HP1 was originally discovered by Tharappel C James and Sarah Elgin in 1986 as a factor in the phenomenon known as position effect variegation in Drosophila melanogaster.
High mobility group box 1 protein,also known as high-mobility group protein 1 (HMG-1) and amphoterin,is a protein that in humans is encoded by the HMGB1 gene.
High-mobility group protein HMG-I/HMG-Y is a protein that in humans is encoded by the HMGA1 gene.
DNA damage-binding protein 2 is a protein that in humans is encoded by the DDB2 gene.
High-mobility group protein B2 also known as high-mobility group protein 2 (HMG-2) is a protein that in humans is encoded by the HMGB2 gene.
Non-histone chromosomal protein HMG-14 is a protein that in humans is encoded by the HMGN1 gene.
Chromodomain-helicase-DNA-binding protein 8 is an enzyme that in humans is encoded by the CHD8 gene.
Daniela Bargellini Rhodes FRS is an Italian structural and molecular biologist. She was a senior scientist at the Laboratory of Molecular Biology in Cambridge,England,where she worked,and later studied for her PhD under the supervision of Nobel laureate Aaron Klug. Continuing her work under the tutelage of Aaron Klug at Cambridge,she was appointed group leader in 1983,obtained tenure in 1987 and was promoted to senior scientist in 1994. Subsequently,she served as director of studies between 2003 and 2006. She has also been visiting professor at both "La Sapienza" in Rome,Italy and the Rockefeller University in NY,USA.
In molecular biology,the HMG-box is a protein domain which is involved in DNA binding. The domain is composed of approximately 75 amino acid residues that collectively mediate the DNA-binding of chromatin-associated high-mobility group proteins. HMG-boxes are present in many transcription factors and chromatin-remodeling complexes,where they can mediate non-sequence or sequence-specific DNA binding.
References
- 1 2 Anon (2017). "Thomas, Dame Jean Olwen" . Who's Who (online Oxford University Press ed.). Oxford: A & C Black. doi:10.1093/ww/9780199540884.013.37399.(Subscription or UK public library membership required.)
- 1 2 Thomas, Jean Olwen (1969). Hydroxyl-carbonyl interaction in cyclic peptides and depsipeptides. jisc.ac.uk (PhD thesis). University College of Swansea. OCLC 502626391. EThOS uk.bl.ethos.639195.
- ↑ Hill, Caroline Susan (1988). Structural studies of sea urchin sperm chromatin. lib.cam.ac.uk (PhD thesis). University of Cambridge. OCLC 53497646. EThOS uk.bl.ethos.305554.
- ↑ St Catharine’s College, Cambridge elects new Master (23 March 2006)
- 1 2 "Swansea University appoints Dame Jean Thomas as chancellor". BBC News. 8 January 2018. Retrieved 9 January 2018.
- ↑ "About LMB". MRC Laboratory of Molecular Biology.
- 1 2 3 4 5 6 "Professor Dame Jean Thomas / Wayne Powell".
- ↑ "The Next Master of St. Catharine's".
- ↑ "Jean Thomas PhD Award".
- ↑ "About Us".
- ↑ "Professor Dame Jean Thomas".
- ↑ "Professor Dame Jean Thomas Appointed as a Trustee".
- ↑ "Society Welcomes New President".
- ↑ "2006 Nobel Prize for Chemistry" (PDF).
- ↑ Watson, M; Stott, K; Thomas, JO (14 December 2007). "Mapping intramolecular interactions between domains in HMGB1 using a tail-truncation approach". Journal of Molecular Biology. 374 (5): 1286–97. doi:10.1016/j.jmb.2007.09.075. PMID 17988686.
- ↑ Cato, L; Watson, M; Stott, K; Thomas, JO (31 December 2008). "The interaction of HMGB1 and linker histones occurs through their acidic and basic tails". Journal of Molecular Biology. 384 (5): 1262–72. doi:10.1016/j.jmb.2008.10.001. PMID 18948112.
- ↑ Stott, K; Watson, M; Howe, F; Grossman, JG; Thomas, JO (12 November 2010). "Tail-mediated collapse of HMGB1 is dynamic and occurs via differential binding of the acidic tail to the A and B domains". Journal of Molecular Biology. 403 (5): 706–22. doi:10.1016/j.jmb.2010.07.045. PMID 20691192.
- ↑ Rowell, JP; Simpson, KL; Stott, K; Watson, M; Thomas, JO (5 December 2012). "HMGB1-facilitated p53 DNA binding occurs via HMG-Box/p53 transactivation domain interaction, regulated by the acidic tail". Structure. 20 (12): 2014–24. doi: 10.1016/j.str.2012.09.004 . PMID 23063560.
- ↑ Stott, K; Watson, M; Bostock, MJ; Mortensen, SA; Travers, A; Grasser, KD; Thomas, JO (24 October 2014). "Structural insights into the mechanism of negative regulation of single-box high mobility group proteins by the acidic tail domain". The Journal of Biological Chemistry. 289 (43): 29817–26. doi: 10.1074/jbc.M114.591115 . PMC 4207994 . PMID 25190813.
- ↑ "Jean Thomas: Department of Biochemistry".
- ↑ Anon (1986). "Dame Jean Thomas DBE FMedSci FRS". royalsociety.org. Royal Society. One or more of the preceding sentences incorporates text from the royalsociety.org website where:
"All text published under the heading 'Biography' on Fellow profile pages is available under Creative Commons Attribution 4.0 International License.” --Royal Society Terms, conditions and policies at the Wayback Machine (archived 2016-11-11)
- ↑ "Professor Dame Jean Thomas".
- ↑ "The Academy of Europe – Academia Europaea".
This article incorporates text available under the CC BY 4.0 license.
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