Histone

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Assembly of histones into a nucleosome

Histones are proteins found in eukaryotic cell nuclei, which package the DNA into structural units called nucleosomes.[1][2] They are the chief protein components of chromatin, the active component of chromosomes.

Histones act as spools around which DNA winds, and play a role in gene regulation. Without histones, the unwound DNA in chromosomes would be very long. For example, each human cell has about 1.8 meters of DNA, but wound on the histones it has about 90 millimeters of chromatin, which, when duplicated and condensed during mitosis, result in about 120 micrometers of chromosomes.[3]

Functions[change | change source]

Compacting DNA strands[change | change source]

Histones act as spools around which DNA winds. This packs in the large genomes of eukaryotes to fit inside cell nuclei. The compacted molecule is 40,000 times shorter than an unpacked molecule.

Chromatin regulation[change | change source]

DNA on outside winding round histone on inside. View from top through helical axis

Histones undergo changes which alter their interaction with DNA and nuclear proteins. Long-term changes in histone/DNA interaction cause epigenetic effects. Combinations of modifications are thought to constitute a code, the so-called histone code.[4][5] Histone modifications act in diverse biological processes such as gene regulation, DNA repair and chromosome condensation (mitosis).

Examples[change | change source]

Examples of histone modifications in transcription regulation include:

Type of
modification
Histone
H3K4 H3K9 H3K14 H3K27 H3K79 H4K20 H2BK5
mono-methylation activation[6] activation[7] activation[7] activation[7][8] activation[7] activation[7]
di-methylation repression[9] repression[9] activation[8]
tri-methylation activation[10] repression[7] repression[7] activation,[8]
repression[7]
repression[9]
acetylation activation[10] activation[10]

History[change | change source]

Histones were discovered in 1884 by Albrecht Kossel. The word "histone" dates from the late 19th century and is from the German "Histon", of uncertain origin: perhaps from Greek histanai or from histos. Until the early 1990s, histones were dismissed as merely packing material for nuclear DNA. During the early 1990s, the regulatory functions of histones were discovered.[11]

The discovery of the H5 histone appears to date back to 1970's.[12][13]

Conservation across species[change | change source]

Histones are found in the nuclei of eukaryotic cells, and in certain Archaea, namely Euryarchaea, but not in bacteria. Histone proteins are among the most highly conserved proteins in eukaryotes,[14] which suggests they are vital to the biology of the nucleus.[2]:939 In contrast, mature sperm cells largely use protamines to package their genomic DNA, most likely to achieve an even higher packaging ratio.[15]

Core histones are highly conserved proteins, that is, there are very few differences among the amino acid sequences of the histone proteins of different species. Linker histone usually has more than one form within a species and is also less conserved than the core histones.

References[change | change source]

  1. Youngson, Robert M. (2006). Collins dictionary of human biology. Glasgow: HarperCollins. ISBN 0-00-722134-7.
  2. 2.0 2.1 Cox, Michael; Nelson, David R.; Lehninger, Albert L (2005). Lehninger principles of biochemistry. San Francisco: W.H. Freeman. ISBN 0-7167-4339-6.
  3. Redon C, Pilch D, Rogakou E, Sedelnikova O, Newrock K, Bonner W (April 2002). "Histone H2A variants H2AX and H2AZ". Curr. Opin. Genet. Dev. 12 (2): 162–9. doi:10.1016/S0959-437X(02)00282-4. PMID 11893489.
  4. Strahl BD, Allis CD (Jan 2000). "The language of covalent histone modifications". Nature 403 (6765): 41–5. doi:10.1038/47412. PMID 10638745.
  5. Jenuwein T, Allis CD (Aug 2001). "Translating the histone code". Science 293 (5532): 1074–80. doi:10.1126/science.1063127. PMID 11498575.
  6. Benevolenskaya EV (August 2007). "Histone H3K4 demethylases are essential in development and differentiation". Biochem. Cell Biol. 85 (4): 435–43. doi:10.1139/o07-057. PMID 17713579.
  7. 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 Barski A, Cuddapah S, Cui K, Roh TY, Schones DE, Wang Z, Wei G, Chepelev I, Zhao K (May 2007). "High-resolution profiling of histone methylations in the human genome". Cell 129 (4): 823–37. doi:10.1016/j.cell.2007.05.009. PMID 17512414.
  8. 8.0 8.1 8.2 Steger DJ, Lefterova MI, Ying L, Stonestrom AJ, Schupp M, Zhuo D, Vakoc AL, Kim JE, Chen J, Lazar MA, Blobel GA, Vakoc CR (April 2008). "DOT1L/KMT4 recruitment and H3K79 methylation are ubiquitously coupled with gene transcription in mammalian cells". Mol. Cell. Biol. 28 (8): 2825–39. doi:10.1128/MCB.02076-07. PMC 2293113. PMID 18285465.
  9. 9.0 9.1 9.2 Rosenfeld JA, Wang Z, Schones DE, Zhao K, DeSalle R, Zhang MQ (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.
  10. 10.0 10.1 10.2 Koch CM, Andrews RM, Flicek P, Dillon SC, Karaöz U, Clelland GK, Wilcox S, Beare DM, Fowler JC, Couttet P, James KD, Lefebvre GC, Bruce AW, Dovey OM, Ellis PD, Dhami P, Langford CF, Weng Z, Birney E, Carter NP, Vetrie D, Dunham I (June 2007). "The landscape of histone modifications across 1% of the human genome in five human cell lines". Genome Res. 17 (6): 691–707. doi:10.1101/gr.5704207. PMC 1891331. PMID 17567990.
  11. Hulton CS, Seirafi A, Hinton JC, Sidebotham JM, Waddell L, Pavitt GD, Owen-Hughes T, Spassky A, Buc H, Higgins CF (Nov 1990). "Histone-like protein H1 (H-NS), DNA supercoiling, and gene expression in bacteria". Cell 63 (3): 631–42. doi:10.1016/0092-8674(90)90458-Q. PMID 2171779.
  12. Crane-Robinson C, Dancy SE, Bradbury EM, Garel A, Kovacs AM, Champagne M, Daune M (August 1976). "Structural studies of chicken erythrocyte histone H5". Eur. J. Biochem. 67 (2): 379–88. doi:10.1111/j.1432-1033.1976.tb10702.x. PMID 964248.
  13. Aviles FJ, Chapman GE, Kneale GG, Crane-Robinson C, Bradbury EM (August 1978). "The conformation of histone H5. Isolation and characterisation of the globular segment". Eur. J. Biochem. 88 (2): 363–71. doi:10.1111/j.1432-1033.1978.tb12457.x. PMID 689022.
  14. Means: few or no changes between species
  15. Clarke HJ (1992). "Nuclear and chromatin composition of mammalian gametes and early embryos". Biochem. Cell Biol. 70 (10-11): 856–66. doi:10.1139/o92-134. PMID 1297351.