分子生物学分子生物学 (8).pdf

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1、Chapter 5Regulation of Gene Expression5.2 Mechanism of gene expression regulation in prokaryotes(Regulation of transcription initiation)5.2.1 factor and regulation of transcription initiationcore enzymeholoenzyme It Regulates the binding of RNA polymerase tospecific DNA region;It ensures the stable

2、binding of RNA polymeraseto a specific promoter region.(1)factorDifferent factors determine the specificrecognition and binding of RNA polymerase toone or one set of promoter sequences.The first discovered factor：70Newly discovered factors：32、54、28(2)Promoter sequencesTranscription start points-35 s

3、equences-10sequencesTTGACATTAACTTTTACATATGATTTTACATATGTTTTGATATATAATCTGACGTACTGTN17N16N17N16N16N7N7N6N7N6AAAAAtrptRNATyrlacrecAAra BADTTGACATATAATConsensus sequencesThe common sequences determinetranscriptionalactivity of promoter.Some specific factors(proteins)ensure the specificrecognition and bin

4、ding ability of RNA polymeraseto one or a set of promoter sequences.5.2.2 Negative regulation of transcription initiation in prokaryotes.Lactose operon(lac)is the classic model ofnegative regulation of gene transcription inprokaryotes.Structure of lactose operon Structural genesZ：beta galactosidase

5、Y：lactose permeaseA：galactoside trans-acetylaseRegulatory sitesCAP binding sitePromoterOperatorZYAOPDNARepressor proteinmRNARepressor protein IDNAZYAOPWith glucose,no lactoseNegative regulation of repressor proteins Repressor genemRNARepressor protein IDNAZYAOPpolWith glucose,no lactoseNegative regu

6、lation of repressor protein Repressor genemRNARepressor protein No glucose,with lactoseIDNAZYAOPpolInitiating transcriptionLactoseGalactose-galactosidasemRNARepressor protein IDNAZYAOPpolInitiating transcriptionmRNALactose-galactosidaseGalactoseNo glucose,with lactoseThe operator region that binds t

7、o repressor protein Icontains an reverse repeat sequence anda typicalDNA structure that can specifically bind to protein.-10+1+10+20+30.5ATGTTGTGTGGAATTGTGAGCGGATAACAATTTCACACAGGAA33TACAACACACCTTAACACTCGCCTATTGTTAAAGTGTGTCCTT 5The position of operator element in operon required forbinding of repress

8、or protein I,locates at-7 to+28,whilethe area occupied by RNA polymerase is from-35 to+20.Obviously,there is partial overlap between them.So thebinding of repressor protein and RNA polymerase to lacoperator/promoter region is exclusive to each other.5.2.3 Positive regulation of transcription initiat

9、ionArabinose operon is a classic example of positive regulationThe diagram of arabinose operonRegulation of AraC on arabinose operon5.2.4 Combinant regulation of transcription initiationIn many operons of E.coli,gene transcriptionis not only regulated by a single factor,but isregulated combinantly b

10、y negative and positiveregulators.Glucose metabolism related operon,such aslactose operon.Transcriptional activity increased by 50 times.No glucose,high cAMPconcentrationPositive regulation of CAPin lactose operonZYAOPDNACAPCAPCAPCAPCAPCAPWith glucose,low cAMPconcentrationThe regulation ofrepressor proteinand cAMP-CAP onthe transcription oflactose operon.When lactose exists alone,bacteria use lactoseas carbonic source;if glucose or glucose/lactosecoexists,bacteria use glucose preferentially.The inhibition of glucose on lac operon is calledcatabolite repression.22