原核与真核基因表达比较.ppt

TranscriptionalRegulation Theregulationoftranscriptionisoneofthemostimportantwaysinwhichgenesareregulated ProkaryotesandEukaryotesDiffer nucleosome ProkaryotesandEukaryotesDiffer Thereisafundamentallydifferentlogicofgeneregulationinbacteriaandeukaryotes Inbacteria thereisaactivegroundstateandgenesareoftenregulatedbyrepression ProkaryotesandEukaryotesDiffer Whileeukaryoteshaveaninactivegroundstateandgenesaretypicallyregulatedbyactivation AllostericRegulation Smallmoleculeeffectors 效应物 canaltertheactivityoftranscriptionfactors ThelacOperon Thelacoperonwasoneofthefirstgeneticregulatorysystemstobeunderstoodindetail Thelacoperonisresponsibleforlactoseutilization anditisonlyactivewhenlactose orrelated galactosides arepresent Lactoseandb Galactosidease 半乳糖 葡萄糖 乳糖 半乳糖苷酶 透性酶 半乳糖苷转乙酰酶 异丙基 D 硫代半乳糖苷 甘油 葡萄糖 MutationsinthelacOperator lacOcmutantshaveanalteredsequencethatdoesnotallowtherepressortobind Thisresultsinacis actingconstitutivephenotype MutationsinthelacRepressor Incontrast lacImutants whichlackrepressoractivity canbecomplementedinmerozygotes Thus lacImutantsaretrans acting MutationsinthelacRepressor lacIsmutants inwhichtherepressorcannotbindtotheinducer areuninduciblemutants TheselacImutantsarealsotrans acting TheCorePromoter Thecorepromotersequenceswesawinourpreviousdiscussionofprokaryotictranscriptioncanbeshowntohaveanimpactontranscriptionalactivity GlucoseRepression Thelacoperonisalsoregulatedbyglucoserepression itisonlyactivewhenlactoseispresentandglucoseisabsent Thisisbecauseglucoseisapreferredcarbonsource Glucoseregulationisindirect sinceitinvolvesthesecondmessengercAMP cyclicAMP ThecAMPsignaltellsthecellthatglucoseisabsent 降解物激活蛋白 CAPProteinBendsDNA WhentheCAP cAMPcomplexbindsDNAitcausestheDNAtobend ThisbendingappearstobethecauseofthetranscriptionalactivationbytheCAP cAMPcomplex ThetrpOperon Thetrpoperonisresponsiblefortryptophanbiosynthesis Whenwouldweexpecttoseetrpoperonactivity 分支酸 邻胺苯甲酸 磷酸核糖 吲哚 ThetrpOperon Thetrpoperonisactivewhentryptophanisabsent Tryptophanactsasasmallmoleculeco repressor bindingthetrprepressorandcausingthetrprepressortobindDNAintheboundstate ThetrpOperon Thetrpoperonisalsoregulatedbyattenuation Attenuationisaninteractionbetweentranscriptionandtranslation Thereisashortopenreadingframe ORF upstreamofthetrpgenes ThisORFhastwoTrpcodons Ifaribosomestallsonthesecodons transcriptioncontinues Otherwise itisterminated EukaryoticPromoters Eukaryoticpromotersaremuchmorecomplexandtheelementspresentaremuchmorevariable TheTATAboxisoneofthemostimportant andthemajorityofpromotershaveit TheCCAATandGCboxesarepresentinmanypromoters buttheirpresenceismorevariable EukaryoticPromoters Theseboxescanalsobedefinedmutationally Morerecently computationhasbeenusedtodefinethem Enhancers Enhancersareregulatorysitesthatcanbequitefarawayintermsofthesequence TheEnhanceosome ReporterGenes Areportergenelike galactosidasecanbeusedtostudydifferentenhancerelements Here Drosophilaembryosstainedfor galactivityareshownregulatedbydppenhancerelementsareshown LateralEctoderm LE ImaginalDisc ID ChromatinandTranscription ThecompactionofeukaryoticDNAintochromatinhasaprofoundimpactontranscriptionalregulation DosageCompensation Femalemammalsaremosaics withoneoftheirtwoXchromosomesinactivated Inactivationinvolvesthetranscriptionofanon codinggenecalledXIST Otherorganismshaveothermeansofdosagecompensation suchashypertranscriptionofthemaleX linkedgenes Drosophila orreducingX linkedtranscription C eleganshermaphrodites Prader Willi AngelmanSyndromes Bothofthesegeneticdisordersarecausedbydeletionofasegmentofchromosome15 However thesyndromesdiffer Prader WilliSyndrome obesity mentalretardation shortstature AngelmanSyndrome uncontrollablelaughter jerky抽筋的movements andothermotorandmentalsymptoms Thesyndromethatdevelopsdependsupontheparentthatprovidedthemutantchromosome PWS AS PWSMousemodel ASMousemodel FromAnnuRevGenomics HumGenet Prader Willi AngelmanSyndromes Prader WilliSyndrome developswhentheabnormalcopyofchromosome15isinheritedfromthefather AngelmanSyndrome developswhentheabnormalcopyofchromosome15isinheritedfromthemother Thedifferencesreflectthefactthatsomelociareimprinted soonlythealleleinheritedfromoneparentisexpressed Thechromosome15regioncontainsgeneswithbothmaternalandpaternalimprinting Imprinting Imprintingisanothertypeofepigeneticregulation 表观遗传调控 inwhichtheparentthatdonatesanalleledetermineswhetheritisactive ThesilencedallelehasspecificchangesinDNAmethylationthatareestablishedintheparentsgermline ChromatinRemodeling Yeastmutantsthatcannotchangematingtypeorfermentsucrose蔗糖 swiandsnfmutants wereidentifiedManyfactorsspecifictomatingtypeswitchingortheregulationofinvertasewereidentified butoneverygeneraltranscriptionfactor SWI SNF wasidentified ThisfactormovesnucleosomesawayfromtheTATAboxofgenes PerturbingHistoneLevels ChangingtheamountsofhistoneH4canaltergeneexpressionglobally IfwecomplementahistoneH4mutantwithaplasmidthathasH4underGALgenecontrolitispossibletodepletehistonesbyshiftingthecellstoglucosemedium Histonedepletionactivatesgenesthatareinducible HistoneModification JustasDNAcanbemodifiedbymethylation histonescanbemodifiedbymethylationandacetylation Acetylationisbetterstudied anditiscorrelatedwithgeneactivation Sometranscriptionfactors likeGCN5 arehistoneacetyltransferases Repressors likeRPD3 arehistonedeacetylases TheEnhanceosome Theenhanceosomewillacttorecruithis