Heterochromatin Protein 1

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chromobox homolog 5
Alt. symbolsHP1-alpha
Other data
LocusChr. 12 q13.13
chromobox homolog 1
Alt. symbolsHP1-beta
Other data
LocusChr. 17 q21.32
chromobox homolog 3
Alt. symbolsHP1-gamma
Other data
LocusChr. 7 p21-15

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The family of Heterochromatin Protein 1 (HP1) ("Chromobox Homolog", CBX) are highly conserved adapter molecules, which have important functions in the cell nucleus. These functions include gene repression by heterochromatin formation, transcriptional activation, regulation of binding of cohesin complexes to centromere, sequesteration of genes to nuclear periphery, transcriptional arrest, maintenance of heterochromatin integrity, gene repression at single nucleosome level and gene repression by heterochromatization of euchromatin. 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 (silent information regulatory) proteins are in action. Members of the HP1 family are characterized by two conserved domains: an N-terminal chromodomain and a C-terminal chromoshadow domain, which are separated by an Hinge Region in between. HP1 is also found at euchromatic sites, where its binding correlates with the repression of an increasing number of genes. HP1 was originally discovered in 1986 as an important factor in the phenomenon known as position effect variegation in Drosophila melanogaster.[1][2]


Three different isoforms of HP1 are found in Drosophila melanogaster, HP1a, HP1b and HP1c. Subsequently homologues of HP1 were also discovered in S. pombe (Swi6), Xenopus (Xhp1α and Xhp1γ) and Chicken (CHCB1, CHCB2 and CHCB3). In mammals,[3] there are three isoforms termed HP1α, HP1β and HP1γ each encoded by different genes.


HP1β interacts with the Histone-Methyltransferase (HMTase) Suv(3-9)h1 and is a component of both pericentric and telomeric heterochromatin.[4][5][6] HP1β is a dosage-dependent modifier of pericentric heterochromatin-induced silencing[7] and silencing is thought to involve a dynamic association of the HP1β chromodomain with the tri-methylated Histone H3 Me(3)K9H3.

HP1 Interacting Proteins

HP1 seems to interact with numerous other proteins/molecules with different cellular functions in different organisms. Some of these HP1 interacting partners are: Histone H1, Histone H3, Methylated K9 Histone H3, Histone H4, Histone methyltransferase, DNA methyltransferase, Methyl CpG binding protein MeCP2

See also


  1. James, T.C. & S.C Elgin (1986). "Identification of a nonhistone chromosomal protein associated with heterochromatin in Drosophila melanogaster and its gene". Mol. Cell Biol. 6: 3862–3872. PMID 3099166.
  2. Eissenberg, J.C., James, T.C., Foster-Hartnett, D.M., Hartnett, T., Ngan, V.K.W., Craig, C., Elgin, S.C.R. (1990). "Mutation in a heterochromatin-specific chromosomal protein are associated with suppression of position-effect variegation in D. melanogaster". J. Cell Biol. 111 (5/2): 5a. PMID 2124708.
  3. Singh PB, Miller JR, Pearce J, Kothary R, Burton RD, Paro R, James TC, Gaunt SJ. (1991). "A sequence motif found in a Drosophila heterochromatin protein is conserved in animals and plants". Nucleic Acids Res. 19 (4): 789–94. doi:10.1093/nar/19.4.789. PMID 1708124. Unknown parameter |month= ignored (help)
  4. Aagaard L, Laible G, Selenko P, Schmid M, Dorn R, Schotta G, Kuhfittig S, Wolf A, Lebersorger A, Singh PB, Reuter G, Jenuwein T. (1999). "Functional mammalian homologues of the Drosophila PEV-modifier Su(var)3-9 encode centromere-associated proteins which complex with the heterochromatin component M31". EMBO J. 18 (7): 1923–38. doi:10.1093/emboj/18.7.1923. PMID 10202156. Unknown parameter |month= ignored (help)
  5. Wreggett KA, Hill F, James PS, Hutchings A, Butcher GW, Singh PB (1994). "A mammalian homologue of Drosophila heterochromatin protein 1 (HP1) is a component of constitutive heterochromatin". Cytogenet. Cell Genet. 66 (2): 99–103. doi:10.1159/000133676. PMID 8287692.
  6. Sharma GG, Hwang KK, Pandita RK, Gupta A, Dhar S, Parenteau J, Agarwal M, Worman HJ, Wellinger RJ, Pandita TK. (2003). "Human heterochromatin protein 1 isoforms HP1(Hsalpha) and HP1(Hsbeta) interfere with hTERT-telomere interactions and correlate with changes in cell growth and response to ionizing radiation". Mol. Cell Biol. 23 (22): 8363–76. doi:10.1128/MCB.23.22.8363-8376.2003. PMID 14585993. Unknown parameter |month= ignored (help)
  7. Festenstein R, Sharghi-Namini S, Fox M, Roderick K, Tolaini M, Norton T, Saveliev A, Kioussis D, Singh P (1999). "Heterochromatin protein 1 modifies mammalian PEV in a dose- and chromosomal-context-dependent manner". Nat. Genet. 23 (4): 457–61. doi:10.1038/70579. PMID 10581035. Unknown parameter |month= ignored (help)

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