UniProtSummary | Function:Corecomponentofnucleosome.NucleosomeswrapandcompactDNAintochromatin,limitingDNAaccessibilitytothecellularmachinerieswhichrequireDNAasatemplate.Histonestherebyplayacentralroleintranscriptionregulation,DNArepair,DNAreplicationandchromosomalstABIlity.DNAaccessibilityisregulatedviaacomplexsetofpost-translationalmodificationsofhistones,alsocalledhistonecode,andnucleosomeremodeling. Subunitstructure:ThenucleosomeisahistoneoctamercontainingtwomoleculeseachofH2A,H2B,H3andH4assembledinoneH3-H4heterotetramerandtwoH2A-H2Bheterodimers.Theoctamerwrapsapproximately147bpofDNA. Subcellularlocation:Nucleus. Post-translationalmodification:AcetylationatLys-6(H4K5ac),Lys-9(H4K8ac),Lys-13(H4K12ac)andLys-17(H4K16ac)occursincodingregionsofthegenomebutnotinheterochromatin. CitrullinationatArg-4(H4R3ci)byPADI4impairsmethylation. MonomethylationatArg-4(H4R3me1)byPRMT1favorsacetylationatLys-9(H4K8ac)andLys-13(H4K12ac).DemethylationisperformedbyJMJD6. SymmetricdimethylationonArg-4(H4R3me2a)bythePRDM1/PRMT5complexmayplayacrucialroleinthegerm-celllineage. Monomethylated,dimethylatedortrimethylatedatLys-21(H4K20me1,H4K20me2,H4K20me3).MonomethylationisperformedbySET8.TrimethylationisperformedbySUV420H1andSUV420H2andinducesgenesilencing. UbiquitinatedbytheCUL4-DDB-RBX1complexinresponsetoultravioletirradiation.ThismayweakentheinteractionbetweenhistonesandDNAandfacilitateDNAaccessibilitytorepairproteins.MonoubiquitinatedatLys-92ofhistoneH4(H4K91ub1)inresponsetoDNAdamage.TheexactroleofH4K91ub1inDNAdamageresponseisstillunclearbutitmayfunctionasalicensingsignalforadditionalhistoneH4post-translationalmodificationssuchasH4Lys-21methylation(H4K20me). Sumoylated,whichisassociatedwithtranscriptionalrepression. Sequencesimilarities:BelongstothehistoneH4family.
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