原核与真核基因表达比较

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1、TranscriptionalRegulationTheregulationoftranscriptionisoneofthemostimportantwaysinwhichgenesareregulated.ProkaryotesandEukaryotesDiffernucleosomeProkaryotesandEukaryotesDifferThereisafundamentallydifferentlogicofgeneregulationinbacteriaandeukaryotes.Inbacteria,thereisaactivegroun

2、dstateandgenesareoftenregulatedbyrepressionProkaryotesandEukaryotesDifferWhileeukaryoteshaveaninactivegroundstateandgenesaretypicallyregulatedbyactivation.AllostericRegulationSmallmoleculeeffectors(效应物)canaltertheactivityoftranscriptionfactors.ThelacOperonThelacoperonwasoneofthef

3、irstgeneticregulatorysystemstobeunderstoodindetail.Thelacoperonisresponsibleforlactoseutilization,anditisonlyactivewhenlactose(orrelatedßgalactosides)arepresent.Lactoseandb-Galactosidease半乳糖葡萄糖b-GalactosideaseLacZgeneproduct乳糖β-半乳糖苷酶透性酶半乳糖苷转乙酰酶异丙基-β-D-硫代半乳糖苷甘油葡萄糖Mutationsinthelac

4、OperatorlacOcmutantshaveanalteredsequencethatdoesnotallowtherepressortobind.Thisresultsinacis-actingconstitutivephenotype.MutationsinthelacRepressorIncontrast,lacImutants,whichlackrepressoractivity,canbecomplementedinmerozygotes.Thus,lacImutantsaretrans-acting.MutationsinthelacRe

5、pressorlacIsmutants,inwhichtherepressorcannotbindtotheinducer,areuninduciblemutants.TheselacImutantsarealsotrans-acting.TheCorePromoterThecorepromotersequenceswesawinourpreviousdiscussionofprokaryotictranscriptioncanbeshowntohaveanimpactontranscriptionalactivity.GlucoseRepression

6、Thelacoperonisalsoregulatedbyglucoserepression-itisonlyactivewhenlactoseispresentandglucoseisabsent.Thisisbecauseglucoseisapreferredcarbonsource.Glucoseregulationisindirect,sinceitinvolvesthesecondmessengercAMP(cyclicAMP).ThecAMPsignaltellsthecellthatglucoseisabsent.降解物激活蛋白CAPPro

7、teinBendsDNAWhentheCAP-cAMPcomplexbindsDNAitcausestheDNAtobend.ThisbendingappearstobethecauseofthetranscriptionalactivationbytheCAP-cAMPcomplex.ThetrpOperonThetrpoperonisresponsiblefortryptophanbiosynthesis.Whenwouldweexpecttoseetrpoperonactivity?分支酸邻胺苯甲酸磷酸核糖吲哚ThetrpOperonThetrpo

8、peronisactivewhentryptophanisabsent.Tryp