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1、8885d_c28_1081-11192/12/042:28PMPage1081mac76mac76:385_reb:chapter28REGULATIONOFGENEEXPRESSION28.1PrinciplesofGeneRegulation1082protein—hemoglobin—inerythrocytes.Giventhehigh28.2RegulationofGeneExpressioninProkaryotes1092costofproteinsynthesis,regulation
2、ofgeneexpressionisessentialtomakingoptimaluseofavailableenergy.28.3RegulationofGeneExpressioninEukaryotes1102Thecellularconcentrationofaproteinisdeter-minedbyadelicatebalanceofatleastsevenprocesses,eachhavingseveralpotentialpointsofregulation:Thefundamen
3、talproblemofchemicalphysiologyandofembryologyistounderstandwhytissuecellsdonotall1.SynthesisoftheprimaryRNAtranscriptexpress,allthetime,allthepotentialitiesinherentintheir(transcription)genome.2.PosttranscriptionalmodificationofmRNA—FrançoisJacobandJacqu
4、esMonod,3.MessengerRNAdegradationarticleinJournalofMolecularBiology,19614.Proteinsynthesis(translation)5.Posttranslationalmodificationofproteins6.Proteintargetingandtransportfthe4,000orsogenesinthetypicalbacterialOgenome,ortheperhaps35,000genesinthehuman
5、7.Proteindegradationgenome,onlyafractionareexpressedinacellatanygiventime.SomegeneproductsarepresentinverylargeTheseprocessesaresummarizedinFigure28–1.Weamounts:theelongationfactorsrequiredforproteinhaveexaminedseveralofthesemechanismsinprevioussynthesis
6、,forexample,areamongthemostabundantchapters.PosttranscriptionalmodificationofmRNA,byproteinsinbacteria,andribulose1,5-bisphosphateprocessessuchasalternativesplicingpatterns(seecarboxylase/oxygenase(rubisco)ofplantsandphotosyn-Fig.26–19b)orRNAediting(seeB
7、ox27–1),canaffecttheticbacteriais,asfarasweknow,themostabundantwhichproteinsareproducedfromanmRNAtranscriptenzymeinthebiosphere.Othergeneproductsoccurinandinwhatamounts.Avarietyofnucleotidesequencesmuchsmalleramounts;forinstance,acellmaycontaininanmRNAca
8、naffecttherateofitsdegradation(p.onlyafewmoleculesoftheenzymesthatrepairrare1020).ManyfactorsaffecttherateatwhichanmRNADNAlesions.Requirementsforsomegeneproductsistranslatedintoaprotein,aswellastheposttransla-changeovertim
