Histone H3 is one of the five main histones involved in the structure of chromatinineukaryotic cells.^[1]^[2] 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 string' structure. Histone proteins are highly post-translationally modified however Histone H3 is the most extensively modified of the five histones. The term "Histone H3" alone is purposely ambiguous in that it does not distinguish between sequence variants or modification state. Histone H3 is an important protein in the emerging field of epigenetics, where its sequence variants and variable modification states are thought to play a role in the dynamic and long term regulation of genes.

Epigenetics and post-translational modifications[edit]

The N-terminus of H3 protrudes from the globular nucleosome core and is susceptible to post-translational modification that influence cellular processes. These modifications include the covalent attachment of methyl or acetyl groups to lysine and arginine amino acids and the phosphorylation of serineorthreonine. Di- and Tri-methylation of lysine 9 are associated with repression and heterochromatin (see H3K9me2 and H3K9me3), while mono-methylation of K4 (K4 corresponds to lysine residue at 4th position)(see H3K4me1), is associated with active genes.^[3]^[4] Acetylation of histone H3 at several lysine positions in the histone tail is performed by histone acetyltransferase enzymes (HATs). Acetylation of lysine14 is commonly seen in genes that are being actively transcribed into RNA (see H3K14ac).

Sequence variants[edit]

Mammalian cells have seven known sequence variants of histone H3. These are denoted as Histone H3.1, Histone H3.2, Histone H3.3, Histone H3.4 (H3T), Histone H3.5, Histone H3.X and Histone H3.Y but have highly conserved sequences differing only by a few amino acids.^[5]^[6] Histone H3.3 has been found to play an important role in maintaining genome integrity during mammalian development.^[7] Histone variants from different organisms, their classification and variant specific features can be found in "HistoneDB - with Variants" database.

Genetics[edit]

Histone H3s are coded by several genes in the human genome, including:

H3.1: HIST1H3A, HIST1H3B, HIST1H3C, HIST1H3D, HIST1H3E, HIST1H3F, HIST1H3G, HIST1H3H, HIST1H3I, HIST1H3J
H3.2: HIST2H3A, HIST2H3C, HIST2H3D
H3.3: H3F3A, H3F3B

References[edit]

^ Bhasin M, Reinherz EL, Reche PA (2006). "Recognition and classification of histones using support vector machine" (PDF). Journal of Computational Biology. 13 (1): 102–12. doi:10.1089/cmb.2006.13.102. PMID 16472024.

^ Hartl DL, Freifelder D, Snyder LA (1988). Basic Genetics. Boston: Jones and Bartlett Publishers. ISBN 978-0-86720-090-4.

^ Rosenfeld JA, Wang Z, Schones DE, Zhao K, DeSalle R, Zhang MQ (March 2009). "Determination of enriched histone modifications in non-genic portions of the human genome". BMC Genomics. 10: 143. doi:10.1186/1471-2164-10-143. PMC 2667539. PMID 19335899.

^ Lachner M, O'Carroll D, Rea S, Mechtler K, Jenuwein T (Mar 2001). "Methylation of histone H3 lysine 9 creates a binding site for HP1 proteins". Nature. 410 (6824): 116–20. Bibcode:2001Natur.410..116L. doi:10.1038/35065132. PMID 11242053. S2CID 4331863.

^ Marzluff WF, Gongidi P, Woods KR, Jin J, Maltais LJ (Nov 2002). "The human and mouse replication-dependent histone genes". Genomics. 80 (5): 487–98. doi:10.1016/S0888-7543(02)96850-3. PMID 12408966.

^ Hake SB, Garcia BA, Duncan EM, Kauer M, Dellaire G, Shabanowitz J, Bazett-Jones DP, Allis CD, Hunt DF (Jan 2006). "Expression patterns and post-translational modifications associated with mammalian histone H3 variants". The Journal of Biological Chemistry. 281 (1): 559–68. doi:10.1074/jbc.M509266200. PMID 16267050.

^ Jang CW, Shibata Y, Starmer J, Yee D, Magnuson T (Jul 2015). "Histone H3.3 maintains genome integrity during mammalian development". Genes & Development. 29 (13): 1377–92. doi:10.1101/gad.264150.115. PMC 4511213. PMID 26159997.

Cytogenetics: chromosomes

Basic
concepts

Types

Autosome/Sex chromosome (orallosome or heterosome)
Macrochromosome/Microchromosome
Circular chromosome/Linear chromosome
Extra chromosome (or accessory chromosome)
Supernumerary chromosome
A chromosome/B chromosome
Lampbrush chromosome
Polytene chromosome
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Processes
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Histone

Centromere