21807 Ch17
Transcript of 21807 Ch17
-
7/21/2019 21807 Ch17
1/48
Gene Regulation inGene Regulation in
ProkaryotesProkaryotes
-
7/21/2019 21807 Ch17
2/48
Outline of Chapter 16Outline of Chapter 16 There are many steps in gene expression and regulationThere are many steps in gene expression and regulation
can occur at any one of themcan occur at any one of them
Genetic and molecular studies show that most regulationGenetic and molecular studies show that most regulation
affects the initiation of RN transcriptsaffects the initiation of RN transcripts
!tudies of genes for lactose utili"ation!tudies of genes for lactose utili"ation Negati#e regulation $ %locks transcriptionNegati#e regulation $ %locks transcription
Positi#e regulation $ increases transcriptionPositi#e regulation $ increases transcription
&N %inding proteins acting on RN polymerase at promoter are main&N %inding proteins acting on RN polymerase at promoter are main
agents of regulationagents of regulation
ttenuation of expression $ tryptophan pathwayttenuation of expression $ tryptophan pathway Gene expression is fine tuned %y premature termination ofGene expression is fine tuned %y premature termination of
transcriptiontranscription
-
7/21/2019 21807 Ch17
3/48
Outline of Chapter 16Outline of Chapter 16 Glo%al regulatory mechanisms'Glo%al regulatory mechanisms' E.E.coliscolis
response to heat shock is an example of theresponse to heat shock is an example of the
%acterial a%ility to coordinate the expression of%acterial a%ility to coordinate the expression of
different sets of genes dispersed around thedifferent sets of genes dispersed around the
chromosome(chromosome( )icroarray analysis is an important new tool for)icroarray analysis is an important new tool for
detecting changes in gene expression in response todetecting changes in gene expression in response to
en#ironmental changesen#ironmental changes Comprehensi#e example' *owComprehensi#e example' *ow Vibrio choleraeVibrio cholerae
regulate their #irulence genesregulate their #irulence genes
-
7/21/2019 21807 Ch17
4/48
RN polymerase is the key en"ymeRN polymerase is the key en"yme
for transcriptionfor transcription
RN polymerase in#ol#ed in three phases ofRN polymerase in#ol#ed in three phases of
transcriptiontranscription +nitiation $ sigma su%unit , core en"yme -two alpha. one %eta.+nitiation $ sigma su%unit , core en"yme -two alpha. one %eta.
and one %eta/ su%unit0and one %eta/ su%unit0 inds to promoter. unwinds &N. %egins polymeri"ation of %asesinds to promoter. unwinds &N. %egins polymeri"ation of %ases
complementary to &N templatecomplementary to &N template
2longation $ mo#ement away from promoter sigma su%unit2longation $ mo#ement away from promoter sigma su%unit
released. polymeri"ationreleased. polymeri"ation
Termination $signal reached %y RN polymeraseTermination $signal reached %y RN polymerase Rho dependent termination $ Rho factor recogni"es se3uence in mRN.Rho dependent termination $ Rho factor recogni"es se3uence in mRN.
%inds to it. and pulls it away from RN polymerase%inds to it. and pulls it away from RN polymerase
Rho independent termination $ stem loop structure formed %y se3uenceRho independent termination $ stem loop structure formed %y se3uence
of 45 %ases with a run of 6 or more /s signals release of RNof 45 %ases with a run of 6 or more /s signals release of RN
polymerasepolymerase
-
7/21/2019 21807 Ch17
5/48
Fig. 16.2
-
7/21/2019 21807 Ch17
6/48
Translation in prokaryotes starts %efore transcriptionTranslation in prokaryotes starts %efore transcription
endsends
+nitiation sites for translation signal ri%osomes to %ind near 7/+nitiation sites for translation signal ri%osomes to %ind near 7/end of mRN while downstream transcription is still occurringend of mRN while downstream transcription is still occurring
Polycistronic mRNs often lead to the translation of se#eralPolycistronic mRNs often lead to the translation of se#eral
genes at the same time from one mRN transcriptgenes at the same time from one mRN transcript
The regulation of gene expression can occur at manyThe regulation of gene expression can occur at many
stepssteps inding of RN polymerase to promoterinding of RN polymerase to promoter
!hift from initiation to elongation!hift from initiation to elongation
Release of mRN at terminationRelease of mRN at termination
Posttranscriptional sta%ility of mRNPosttranscriptional sta%ility of mRN
2fficiency of ri%osomes to recogni"e translation initiation sites2fficiency of ri%osomes to recogni"e translation initiation sites
!ta%ility of polypeptide product!ta%ility of polypeptide product
-
7/21/2019 21807 Ch17
7/48
The utili"ation of lactose %yThe utili"ation of lactose %yE. coliE. coli''
model system for gene regulation model system for gene regulation
The presence of lactose induces expression of the genesThe presence of lactose induces expression of the genes
re3uired for lactose utili"ationre3uired for lactose utili"ation +nduction+nduction$ stimulation of protein synthesis$ stimulation of protein synthesis
+nducer+nducer$ molecule that stimulates synthesis$ molecule that stimulates synthesis 8actose8actose$ inducer of genes for lactose utili"ation$ inducer of genes for lactose utili"ation
1975s and 1965s $ Golden era of %acterial genetics1975s and 1965s $ Golden era of %acterial genetics d#antages ofd#antages ofE. coliE. coliand lactose utili"ation systemand lactose utili"ation system
Culture large num%ers of %acteria allow isolation of rare mutantsCulture large num%ers of %acteria allow isolation of rare mutants 8actose genes not essential for sur#i#al -can use glucose as car%on8actose genes not essential for sur#i#al -can use glucose as car%on
source0source0
+nduction increases expression 1555 fold making mutant identification+nduction increases expression 1555 fold making mutant identification
easyeasy
Color changes usingColor changes using :galactosidase en"yme -e(g(. OPNG. ;:gal0 make:galactosidase en"yme -e(g(. OPNG. ;:gal0 makemeasurement of expression le#els efficientmeasurement of expression le#els efficient
-
7/21/2019 21807 Ch17
8/48
Coordinate repression and induction of three genesCoordinate repression and induction of three genes
re#ealed %y studies of lactose:utili"ation mutantsre#ealed %y studies of lactose:utili"ation mutants
-
7/21/2019 21807 Ch17
9/48
Complementation nalysis of mutants identifiesComplementation nalysis of mutants identifies
lactose utili"ation geneslactose utili"ation genes
)onod et al( isolated many 8ac)onod et al( isolated many 8ac::mutants una%le tomutants una%le to
utili"e lactoseutili"e lactose Complementation analysis identified three genesComplementation analysis identified three genes
-lac>. lac?. and lac0 in a tightly linked cluster-lac>. lac?. and lac0 in a tightly linked cluster
Fig. 16.5
-
7/21/2019 21807 Ch17
10/48
2xperimental e#idence for repressor protein2xperimental e#idence for repressor protein
+solated mutant in+solated mutant in lacIlacIgenegene
Constituti#eConstituti#emutant $ synthesi"edmutant $ synthesi"ed ::
galactosidase and lac permease e#en in a%sencegalactosidase and lac permease e#en in a%sence
of lactose -inducer0of lactose -inducer0
lacIlacImust %e amust %e a repressorrepressor$ cells must need$ cells must need lacIlacI
protein product to pre#ent expression ofprotein product to pre#ent expression of lacYlacY
andand lacZlacZin a%sence of inducerin a%sence of inducer
-
7/21/2019 21807 Ch17
11/48
Pa
-
7/21/2019 21807 Ch17
12/48
+nducer releases repressor to trigger+nducer releases repressor to trigger
en"yme synthesisen"yme synthesis
ddition of lactose inducer causedddition of lactose inducer caused $$
galactosidase synthesis to continuegalactosidase synthesis to continue
Conclusion' +nducer %inds to repressor soConclusion' +nducer %inds to repressor so
repressor can not %ind to &Nrepressor can not %ind to &N
llostericllostericeffect : inducer %ound toeffect : inducer %ound to
promotor changes conformation of proteinpromotor changes conformation of protein
so it can not %ind to &Nso it can not %ind to &N
-
7/21/2019 21807 Ch17
13/48
Repressor has %inding domains forRepressor has %inding domains for
operator and for the induceroperator and for the inducer
Fig. 16.7
-
7/21/2019 21807 Ch17
14/48
Changes in the operator can alsoChanges in the operator can also
affect repressor acti#ityaffect repressor acti#ity
Fig. 16.8
-
7/21/2019 21807 Ch17
15/48
Proteins act inProteins act in transtrans
&N sites act only in&N sites act only in ciscis
TransTransacting elementsacting elementscan diffuse throughcan diffuse through
cytoplasm and act at target &N sites oncytoplasm and act at target &N sites on
any &N molecule in cellany &N molecule in cell
CisCisacting elementsacting elementscan only influencecan only influence
expression of ad@acent genes on same &Nexpression of ad@acent genes on same &N
moleculemolecule
-
7/21/2019 21807 Ch17
16/48
Three experiments elucidateThree experiments elucidate ciscisandand transtrans
acting elements using =/ plasmidacting elements using =/ plasmid
+nduci%le synthesis+nduci%le synthesis
lacIlacI,,gene encodes agene encodes a
diffusi%le element thatdiffusi%le element that
acts inacts in transtrans%y%y
%inding to any%inding to any
operator it encountersoperator it encounters
regardless ofregardless ofchromosomal locationchromosomal location
Insert Figure 16.9ahere
Fi . 16.9 a
-
7/21/2019 21807 Ch17
17/48
Noninduci%leNoninduci%le
ll operator sites -O,0ll operator sites -O,0e#entually occupied %ye#entually occupied %ysuperrepressorsuperrepressor
lacIlacIsupperrepressor cansupperrepressor cannot %ind inducernot %ind inducer lacIlacIss mutant encodes amutant encodes a
diffusi%le element thatdiffusi%le element that%inds to operator%inds to operatorregardless of chromosomalregardless of chromosomallocation -trans actinglocation -trans actingelement0element0
Insert Figure 16.9bhere
Fig. 16.9 b
-
7/21/2019 21807 Ch17
18/48
Constituti#eConstituti#e
Presence of OPresence of O,,plasmidplasmid
does not compensatedoes not compensate
for Ofor Occ
mutation onmutation on%acterial chromosome%acterial chromosome
Operator isOperator is ciscisactingacting
elementelement
Insert Figure 16.9chere
Fig. 16.9 c
-
7/21/2019 21807 Ch17
19/48
The Operon TheoryThe Operon Theory
The playersThe players
laczlacz.. lacYlacY.. lacZlacZgenes that split lactose into glucose and galactosegenes that split lactose into glucose and galactose
Promotor site to which RN polymerase %indsPromotor site to which RN polymerase %inds
cis acting operator sitecis acting operator site
trans:acting repressor that can %ind to operator -encoded %ytrans:acting repressor that can %ind to operator -encoded %y lacIlacIgene0gene0
+nducer that pre#ents repressor from %inding to operator+nducer that pre#ents repressor from %inding to operator
Fi . 16.10 a
-
7/21/2019 21807 Ch17
20/48
The Operon TheoryThe Operon Theory
RepressionRepression +n a%sence of lactose. repressor %inds to operator which+n a%sence of lactose. repressor %inds to operator which
pre#ents transcriptionpre#ents transcription
Negati#e regulatory elementNegati#e regulatory element
Fig. 16.10 b
-
7/21/2019 21807 Ch17
21/48
The Operon TheoryThe Operon Theory
+nduction+nduction 8actose present8actose present
llolactose %inds tollolactose %inds to
repressor(repressor(
Repressor changes shapeRepressor changes shape
and can not %ind toand can not %ind tooperatoroperator
RN polymerase %indsRN polymerase %inds
to promotor andto promotor and
initiates transcription ofinitiates transcription of
polycistronic mRNpolycistronic mRN
Fig. 16.10 c
-
7/21/2019 21807 Ch17
22/48
Positi#e control increasesPositi#e control increases
transcription oftranscription of lacZlacZ.. lacYlacY. and. and lacAlacA c)P %inds toc)P %inds to
CRP -c)PCRP -c)P
receptor protein0receptor protein0
when glucose is lowwhen glucose is low
CRP %inds toCRP %inds to
regulatory regionregulatory region
2nhances acti#ity2nhances acti#ity
of RN polymeraseof RN polymeraseat lac promotorat lac promotor
Fi . 16.11
-
7/21/2019 21807 Ch17
23/48
!ome positi#e regulators increase!ome positi#e regulators increase
transcription of genes in only one pathwaytranscription of genes in only one pathway
AraCAraCis a positi#eis a positi#e
regulator for allregulator for all
ara%inose genesara%inose genes
which %reak downwhich %reak downsugar ara%inosesugar ara%inose
8oss of function8oss of function
mutation results inmutation results in
little or nolittle or noexpression of genesexpression of genes
Fig. 16.12
-
7/21/2019 21807 Ch17
24/48
)olecular studies help fill in details)olecular studies help fill in details
of control mechanismsof control mechanisms Radioacti#e tag attachedRadioacti#e tag attached
to lac repressorto lac repressor Repressor fromRepressor from lacIlacI,,cellscells
purified and mixed withpurified and mixed with
operator &N. cosedimentoperator &N. cosedimentoccurredoccurred
Repressor fromRepressor from lacIlacI,,mixedmixed
with mutant operator &N.with mutant operator &N.
no cosediment occurredno cosediment occurred
Fig. 16.13
-
7/21/2019 21807 Ch17
25/48
)any &N:inding proteins contain)any &N:inding proteins contain
a helix:turn:helix motifa helix:turn:helix motif
TwoTwo AA:helical regions:helical regions
separated %y a turn inseparated %y a turn in
the protein structurethe protein structure
*elix:turn:helix motif*elix:turn:helix motif
fits into ma@or groo#efits into ma@or groo#e
of &Nof &N
)ost repressor)ost repressorproteinsproteins
Fig. 16.14 a
-
7/21/2019 21807 Ch17
26/48
!pecific amino acids in the a:helix determine!pecific amino acids in the a:helix determine
the %inding specificity of repressor proteinsthe %inding specificity of repressor proteins
*y%rid BB:P44 repressor engineered to ha#e amino acid*y%rid BB:P44 repressor engineered to ha#e amino acid
se3uence that will %ind to %acterial #irus BB andse3uence that will %ind to %acterial #irus BB and
%acteriophage P44%acteriophage P44 Fig. 16.14 b
-
7/21/2019 21807 Ch17
27/48
)ost regulatory proteins are)ost regulatory proteins are
oligomericoligomeric
More than one
binding domain
DNase footrint
identifies bindingregion
DNase cannot
digest rotein
co!ered sites
Fig. 16.15 a
-
7/21/2019 21807 Ch17
28/48
The looping of &N is a commonThe looping of &N is a common
feature of regulatory proteinsfeature of regulatory proteins
AraCAraCacts as %oth aacts as %oth arepressor and acti#atorrepressor and acti#ator No ara%inoseNo ara%inose
inding toinding to araOaraOandand
araIaraI11causes looping andcauses looping andpre#ents RN frompre#ents RN fromtranscri%ingtranscri%ing
ra%inose presentra%inose present AraCAraC %inds to%inds to araIaraI11andand
araIaraI44%ot not to%ot not to araOaraO( RN( RNpolymerase interacts withpolymerase interacts witharaCaraCat theat the araIaraIsites andsites andtranscri%es genestranscri%es genes
Fig. 16.16
-
7/21/2019 21807 Ch17
29/48
*ow regulatory proteins interact*ow regulatory proteins interact
with RN polymerasewith RN polymerase
Negati#e regulators -Negati#e regulators -laclacrepressor0repressor0
Physically %lock &N:%inding sites of RNPhysically %lock &N:%inding sites of RN
polymerasepolymerase
Positi#e regulatorsPositi#e regulators
2sta%lish physical contact with RN2sta%lish physical contact with RN
polymerase enhancing en"yme/s a%ility topolymerase enhancing en"yme/s a%ility to
initiate transcriptioninitiate transcription
-
7/21/2019 21807 Ch17
30/48
sing the lac> gene as a reporter ofsing the lac> gene as a reporter of
gene expressiongene expression
Reporter gene $ protein encoding geneReporter gene $ protein encoding gene
whose expression in the cell is 3uantifia%lewhose expression in the cell is 3uantifia%le
%y techni3ues of protein detection(%y techni3ues of protein detection(
=usion of reporter gene to cis acting=usion of reporter gene to cis acting
regulatory regions allows assessment generegulatory regions allows assessment gene
acti#ity %y monitoring amount of reporteracti#ity %y monitoring amount of reporter
gene productgene product
-
7/21/2019 21807 Ch17
31/48
=usion used to perform genetic studies of the=usion used to perform genetic studies of the
regulatory region of gene ;regulatory region of gene ;
Fig. 16.18 a
C iC ti
-
7/21/2019 21807 Ch17
32/48
Creating aCreating a
collection ofcollection of
lac>lac>insertions ininsertions in
thethe
chromosomechromosome
Fig. 16.18 b
-
7/21/2019 21807 Ch17
33/48
se of a fusion tose of a fusion to
o#erproduce a geneo#erproduce a gene
productproduct
Fig. 16.18 c
-
7/21/2019 21807 Ch17
34/48
The attenuation of gene expression' =ine tuning of theThe attenuation of gene expression' =ine tuning of the trptrp
operon through termination of transcriptionoperon through termination of transcription
The presence of tryptophan acti#ates aThe presence of tryptophan acti#ates a
repressor of the trp operonrepressor of the trp operon
trpR gene produces repressortrpR gene produces repressor CorepressorCorepressor$ tryptophan %inds to trp repressor$ tryptophan %inds to trp repressor
allowing it to %ind to operator &N and inhi%itallowing it to %ind to operator &N and inhi%it
transcriptiontranscription
-
7/21/2019 21807 Ch17
35/48
-
7/21/2019 21807 Ch17
36/48
Termination of transcription fineTermination of transcription fine
tunes regulation oftunes regulation of trptrpoperonoperon
trpRtrpR::mutants are not constituti#emutants are not constituti#e Repressor independent change inRepressor independent change in trptrpexpressionexpression
Two alternati#e transcripts lead to differentTwo alternati#e transcripts lead to different
transcriptional outcomestranscriptional outcomes 8eader se3uence can fold in two different sta%le8eader se3uence can fold in two different sta%le
conformationsconformations Tryptophan present $ ri%osome mo#es 3uickly past codons inTryptophan present $ ri%osome mo#es 3uickly past codons in
leader allowing stem:loop to form terminating transcriptionleader allowing stem:loop to form terminating transcription
Tryptophan a%sent $ ri%osome stalls allowing normal stem loopTryptophan a%sent $ ri%osome stalls allowing normal stem loop
structure to form and transcription proceeds normallystructure to form and transcription proceeds normally
-
7/21/2019 21807 Ch17
37/48
-
7/21/2019 21807 Ch17
38/48
Glo%al regulatory mechanisms coordinate theGlo%al regulatory mechanisms coordinate the
expression of many genesexpression of many genes
Normal sigma factor -Normal sigma factor -D5D50 %inds to RN polymerase and0 %inds to RN polymerase and
recogni"es se3uence in promoter to initiate transcriptionrecogni"es se3uence in promoter to initiate transcription
*eat shock disa%les*eat shock disa%les D5D5
Product ofProduct of rpoHrpoHgene.gene. 44%inds to se3uence in promoter of%inds to se3uence in promoter of
heat shock genes when heat stressed and starts transcriptionheat shock genes when heat stressed and starts transcription
Fig. 16.21 a
-
7/21/2019 21807 Ch17
39/48
=actors influencing increase in=actors influencing increase in 44acti#ity after heat shockacti#ity after heat shock
+ncrease in transcription of the rpo* gene+ncrease in transcription of the rpo* gene +ncrease in the translation of+ncrease in the translation of C4C4mRNmRN
stemming from greater sta%ility of rpo* mRNstemming from greater sta%ility of rpo* mRN
+ncrease in the sta%ility and acti#ity of the+ncrease in the sta%ility and acti#ity of the C4C4protein( Chaperones &na
-
7/21/2019 21807 Ch17
40/48
hat ena%les transcription ofhat ena%les transcription of 44during heat shockHduring heat shockH
Normal temperatures.Normal temperatures. rpoHrpoHgene -encodesgene -encodesC4C40 has promoter se3uence recogni"ed %y0 has promoter se3uence recogni"ed %y D5D5
which starts transcriptionwhich starts transcription
*igh temperatures -no*igh temperatures -no D5D5
0 a different promoter0 a different promoter
se3uence of these3uence of the rpoHrpoHgene is recogni"ed %y agene is recogni"ed %y a
different sigma factor.different sigma factor. 4B4B
-
7/21/2019 21807 Ch17
41/48
!ummary!ummary
E. colisE. colisheat shock response is controlled %yheat shock response is controlled %y
alternati#e sigma factors that recogni"e differentalternati#e sigma factors that recogni"e different
promoter se3uencespromoter se3uences
lternati#e sigma factors %ind to RN polymeraselternati#e sigma factors %ind to RN polymerase
as temperatures change to start transcription ofas temperatures change to start transcription of
heat shock proteinsheat shock proteins
The induction of alternati#e sigma factors thatThe induction of alternati#e sigma factors thatrecogni"e different promoter se3uences ser#e asrecogni"e different promoter se3uences ser#e as
glo%al control regulatory mechanisms inglo%al control regulatory mechanisms inE. coliE. coliand many other %acteriaand many other %acteria
-
7/21/2019 21807 Ch17
42/48
)icroarrays $ a tool for unco#ering)icroarrays $ a tool for unco#ering
changes in gene expressionchanges in gene expression
Cellular responses to glo%al en#ironmentalCellular responses to glo%al en#ironmental
changes can %e measured %y microarraychanges can %e measured %y microarray
analysis of mRN isolated from culturesanalysis of mRN isolated from cultures
grown in different en#ironmental conditionsgrown in different en#ironmental conditions Comparisons of wild:type cultures withComparisons of wild:type cultures with
strains containing mutations in keystrains containing mutations in key
regulatory regions help identify genes andregulatory regions help identify genes and
regulatory elements in#ol#ed in response toregulatory elements in#ol#ed in response to
specific en#ironmental changesspecific en#ironmental changes
-
7/21/2019 21807 Ch17
43/48
Fig. 1.13
-
7/21/2019 21807 Ch17
44/48
Regulation of Iirulence Genes inRegulation of Iirulence Genes in V.V.
choleraecholerae
acterial agents of cholera sense changes inacterial agents of cholera sense changes in
en#ironment and transmit signals toen#ironment and transmit signals to
regulators that initiate. enhance. diminish.regulators that initiate. enhance. diminish.
or repress expression of #arious genes(or repress expression of #arious genes(
Three regulatory proteins $ ToxR. Tox!.Three regulatory proteins $ ToxR. Tox!.
and ToxT $ turn on the genes for #irulenceand ToxT $ turn on the genes for #irulence
-
7/21/2019 21807 Ch17
45/48
2xperiments generate model for regulation of2xperiments generate model for regulation of
#irulence genes in#irulence genes in V. choleraeV. cholerae
Cloned two genes encoding su%units ofCloned two genes encoding su%units of
cholera toxin'cholera toxin' ctxActxAandand ctxBctxB
)ade)ade ctxAlacZctxAlacZreporter gene fusionreporter gene fusion
Created #ector li%rary ofCreated #ector li%rary of V. choleraeV. cholerae
genomic &Ngenomic &N
sedsed
E. coliE. coli
to perform geneticto perform genetic
manipulationsmanipulations
-
7/21/2019 21807 Ch17
46/48
+solated a gene that regulates expression of+solated a gene that regulates expression of ctxctxoperonoperon TransformedTransformedE. coliE. colicontainingcontaining ctxlacZctxlacZconstruct with clonesconstruct with clones
containingcontaining V. choleraeV. cholerae&N&N
Clones that contain a positi#e regulator should turn onClones that contain a positi#e regulator should turn on ctxlacZctxlacZconstructconstruct
+dentified+dentified ToxRToxR. a transmem%rane protein. a transmem%rane protein
+dentified+dentified Tox!Tox!. helps. helps ToxRToxRform dimers which helps it %ind to &Nform dimers which helps it %ind to &N
hat genes doeshat genes does ToxRToxRregulateHregulateH
Gene fusions created to constituti#e promoterGene fusions created to constituti#e promoter =usion introduced into strains of=usion introduced into strains of V. choleraeV. choleraewithwith lacZlacZrandomly insertedrandomly inserted
around the genomearound the genome
+dentified intermediate regulator gene+dentified intermediate regulator gene ToxTToxT. a transcriptional acti#ator. a transcriptional acti#ator
that %inds to promoters of many genes. includingthat %inds to promoters of many genes. including ctxctx
ToxRE! or ToxT can acti#ate the ctx genes that produce toxinToxRE! or ToxT can acti#ate the ctx genes that produce toxin
ToxT alone acti#ates additional #irulence genes which encode pili andToxT alone acti#ates additional #irulence genes which encode pili and
other proteinsother proteins
Transcription of ToxT is regulated %y ToxRE!Transcription of ToxT is regulated %y ToxRE!
-
7/21/2019 21807 Ch17
47/48
Fig. 16.22
-
7/21/2019 21807 Ch17
48/48
nanswered Juestions Remainnanswered Juestions Remain
hy is there a cascade -ToxR and ToxT0 ofhy is there a cascade -ToxR and ToxT0 of
regulatory factorsHregulatory factorsH
hat &N se3uence in the promoters doeshat &N se3uence in the promoters does
ToxR recogni"eHToxR recogni"eH hat is the signal that/s makes the cholerahat is the signal that/s makes the cholera
%acteria start to coloni"e the small%acteria start to coloni"e the small
intestineHintestineH *ow does ToxR regulatory protein find*ow does ToxR regulatory protein find
%inding sites on the chromosomeH%inding sites on the chromosomeH