武汉大学：《遗传学》课程教学课件（英文讲稿）Chapter 15 Gene Regulation in Prokaryotes

Chapter 15Gene Regulation in Prokaryotes17-1

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 17-1 Gene Regulation in Prokaryotes Gene Regulation in Prokaryotes Chapter 15 Chapter 15

Sectionsto study15.1Theelements of prokaryotic gene expression15.2Regulation of transcription initiation viaDNA-bindingproteins15.3RNA-mediated mechanisms of gene regulation15.4 Discovering and manipulating bacterial gene regulatorymechanisms17-2

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 17-2 Sections to study Sections to study 15.1 The elements of prokaryotic gene expression 15.1 The elements of prokaryotic gene expression 15.2 Regulation of transcription initiation via 15.2 Regulation of transcription initiation via DNA-binding proteins binding proteins 15.3 RNA 15.3 RNA-mediated mechanisms of gene regulation mediated mechanisms of gene regulation 15.4 Discovering and manipulating bacterial gene regulatory mechanisms

Bacteria respond to environmental changes bychanginggene expressionVibrio cholerae causes choleraAquaticreservoirsOral ingestionofDiarrheacontaminated waterColonizationandorfoodMultiplicationSmall intestine17-3

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 17-3 Bacteria respond to environmental changes by Bacteria respond to environmental changes by changing gene expression changing gene expression Vibrio cholerae causes cholera

15.1Theelements ofprokaryoticgeneexpressionRNA polymeraseand thethreephases oftranscriptionInitiation-sigma subunit+core enzymeBindstopromoter,unwindsDNA,begins polymerization of basesElongation-core enzyme moves away from promoter,sigma subunitreleased,polymerization ofribonucleotides.InitiationElongationRNApolymeraseBa.Sigmaβ'asubunitBmRNAounitleavesB'DNAunwindsmPromoterPromoterTranscriptionstart site

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 17-4 15.1 The elements of prokaryotic gene expression 15.1 The elements of prokaryotic gene expression  RNA polymerase RNA polymerase and the three phases of and the three phases of transcription transcription.  Initiation Initiation – sigma subunit + core enzyme sigma subunit + core enzyme  Binds to promoter, unwinds DNA, begins polymerization of bases Binds to promoter, unwinds DNA, begins polymerization of bases  Elongation Elongation – core enzyme moves away from promoter, sigma subunit core enzyme moves away from promoter, sigma subunit released, polymerization of released, polymerization of ribonucleotides ribonucleotides

TerminationRho-dependent termination-Rho factor recognizes sequence inmRNA,binds to it, and pulls it away from RNA polymerase.Rho-independent termination-stem-loop structure formed bysequence of 20 bases with a run of 6 or more U's signals release ofRNA polymerase.TerminationTerminationorRho-dependentRho-independentStem-loop5mRNAmRNAstructuremRNApulledsignalsawayfromRNArelease ofpolymerasemRNARhofactor17-5

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 17-5  Termination Termination  Rho-dependent termination dependent termination – Rho factor recognizes sequence in Rho factor recognizes sequence in mRNA, binds to it, and pulls it away from RNA polymerase. mRNA, binds to it, and pulls it away from RNA polymerase.  Rho-independent termination independent termination – stem-loop structure formed by loop structure formed by sequence of 20 bases with a run of 6 or more U sequence of 20 bases with a run of 6 or more U’s signals release of s signals release of RNA polymerase. RNA polymerase

Polycistronic mRNA:One mRNA contains the information ofseveral genes.Translation in prokaryotes begins before transcription ends!Initiation sites for translation signal ribosomes to bind near 5'end ofmRNA while downstream transcription is still occurringRibosomes can initiate translation at several positions along a singlemRNA.FustThirdSecondParypeptidePolypepticePorypepliceFibosameLSS?StruduralStruciuralStnuciuiralGene1Gene2Gene3fnitiatlonTeminationSileTerminationTermnaticnSignalSignalSignal17-6

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 17-6  Polycistronic Polycistronic mRNA: One mRNA contains the information of : One mRNA contains the information of several genes. several genes.  Translation Translation in prokaryotes begins before in prokaryotes begins before transcription transcription ends!  Initiation sites for translation signal Initiation sites for translation signal ribosomes ribosomes to bind near 5 to bind near 5’ end of mRNA while downstream transcription is still occurring. mRNA while downstream transcription is still occurring.  Ribosomes Ribosomes can initiate translation at several positions along a single can initiate translation at several positions along a single mRNA

The regulation of gene expression can occur at many stepsTranscriptioninitiationShift from initiation to elongationRelease of mRNA at terminationStabilityof mRNAEfficiency of ribosomes to recognize translation initiation sitesStability of polypeptideproduct17-7

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 17-7  Transcription initiation Transcription initiation  Shift from initiation to elongation Shift from initiation to elongation  Release of mRNA at termination Release of mRNA at termination  Stability of mRNA Stability of mRNA  Efficiency of Efficiency of ribosomes ribosomes to recognize translation initiation sites to recognize translation initiation sites  Stability of polypeptide product Stability of polypeptide product The regulation of gene expression can occur at many steps The regulation of gene expression can occur at many steps

15.2Regulation of transcription initiation viaDNA-bindingproteinsA model system for studying gene regulation:The utilization of lactose by E. coli100()8060Jacques Monod's“"bi-phasic"40growth curve2000Co8Time (hours)17-8

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 17-8 15.2 Regulation of transcription initiation via 15.2 Regulation of transcription initiation via DNA-binding proteins binding proteins A model system for studying gene regulation: A model system for studying gene regulation: The utilization of lactose by The utilization of lactose by E. coli E. coli Jacques Monod's “bi-phasic” growth curve

Bacteria grown with two different sugars often displayed twophases ofgrowth.PhaseIPhase IUselactoseUse glucoseGlucoseLactose17-9

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 17-9 Bacteria grown with two diffe Bacteria grown with two different sugars often displayed two rent sugars often displayed two phases of growth. phases of growth. Lactose Glucose Phase I Use glucose Phase II Use lactose

The presence of lactosePeriplasmLactose0000000induces expression ofInnerPermeasePermeasethe genes reguired formembranelactose utilization00000Induction:A process byInsideof cellHOCH2which a signal inducesHOOHexpression ofa gene orOHset of genes.HOCH2OHHOOHOβ-GalactosidaseGalactoseInducer:The moleculeOHOHOHHOCH2H20responsiblefortheOHOHHOCH2induction of geneLactoseOHexpression.HOOHGlucoseFig15.217-10

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 17-10  The presence of lactose The presence of lactose induces induces expression of expression of the genes required for the genes required for lactose utilization lactose utilization  Induction Induction: A process by : A process by which a signal induces which a signal induces expression of a gene or expression of a gene or set of genes. set of genes.  Inducer Inducer: The molecule : The molecule responsible for the responsible for the induction of gene induction of gene expression. expression. Fig 15.2