《分子生物学》第17章 真核生物的基因调控（英文教学课件）非AI生成 (2).ppt

HP1proteinisacomponentofheterochromatininDrosophilathatbindstomethylatedresidueinhistoneH3.SuchahistonemodificationisproducedbySu(Var)3-9.Differenttypesofmodificationatthehistonescanbeinvolvedindistinctgeneregulation.Whatwillhappenwhenmultipleformsofmodificationoccur?---A“HistoneCode”hypothesis.*Box17-4Isthereahistonecode?Accordingtothisidea,differentpatternsofmodificationonhistonetailscanbe“read”tomeandifferentthings.The“meaning”wouldbetheresultofthedirecteffectsofthesemodificationsonchromatindensityandform.Butinaddition,theparticularpatternofmodificationsatanygivenlocationwouldrecruitspecificproteins.*6-3.DNAMethylationIsAssociatedwithSilencedGenesinMammaliancells.Topic6:Gene“Silencing”byModificationofHistonesandDNADNA甲基化与哺乳动物细胞的沉默基因相关联。【注DNA甲基化不是组蛋白甲基化】GATCSomemammaliangenesarekeptsilentbymethylationofnearbyDNAsequences.*LargeregionsofmammaliangenomearemarkedbymethylationofDNAsequences,whichisoftenseeninheterochromaticregions.ThemethylatedDNAsequencesareoftenrecognizedbyDNA-bindingproteins(suchasMeCP2)thatrecruithistonedeacetylasesandhistonemethylases,whichthenmodifynearbychromatin.Thus,methylationofDNAcanmarksiteswhereheterochromatinsubsequentlyforms(Fig.17-25).*Fig.17-25SwitchingageneoffthroughDNAmethylationandthesubsequenthistonemodification*****DNAmethylationliesattheheartofImprintingImprinting-inadiploidcell,onecopyofagenefromthefatherormotherisexpressedwhiletheothercopyissilenced.Twowell-studiedexamples:humanH19andinsulin-likegrowthfactor2(Igf2)genes******Figure17-26ImprintingEnhancer:activatebothgenetranscriptionICR:aninsulatorbindsCTCFproteinandblockstheactivityoftheenhanceronIgf2.MethylationofICRallowstheenhancertoac