The lactose (lac) operon - an example for prokaryotic gene regulation.
-
Upload
phebe-knight -
Category
Documents
-
view
246 -
download
9
Transcript of The lactose (lac) operon - an example for prokaryotic gene regulation.
The lactose (lac) operonThe lactose (lac) operon
- an example for prokaryotic gene regulation- an example for prokaryotic gene regulation
19.
LCT and MCM 6 genesLCT and MCM 6 genes
Breakdown of lactosein human
Breakdown of lactosein human
Nobel prize for the discovery of lac operonNobel prize for the discovery of lac operon - 1965- 1965
Francois Jacob Jacques MonodFrancois Jacob Jacques Monod
Pasteur Institute, Paris, FrancePasteur Institute, Paris, France
1.
DNA lacZ
repressor CAP site RNA pol operator structural genes terminator
lacI O lacY
lacA
C E
promoter
P
Cytoplasm cell wall outer world
promoter Structural genes DNAT
catabolit activator protein binding site
E. coli DNA
binding site
operon
The structure of lac operonThe structure of lac operon2.
Structure lac operonStructure lac operon 3.
DNA DNAlacZ lacI O lacY
lacA
C E P
repressor CAP site entry site operator structural genes terminator
T
polrep
RRepressionepressionRRepressionepression
rep: repressorpol: RNA polymerase
4.
DNA DNAlacZ lacI O lacY
lacA
C E P
rep
lactose
galactose
glucose
repressor CAP site entry site operator structural genes terminator
T
rep: repressorpol: RNA polymerase
5.
InductionInductionInductionInduction
DNA DNAlacZ lacI O lacY
lacA
C E P
trans-acetylase
permease
rep
b-gal
repressor CAP site entry site operator structural genes terminator
T
pol
rep: repressorpol: RNA polymerase
5.
InductionInductionInductionInduction
DNA DNAlacZ lacI O lacY
lacA
C E P
CA
P
cAMP No glucose
repressor CAP site entry site operator structural genes terminator
T
CAP: catabolite activator protein
6.
ActivationActivationActivationActivation
DNA DNAlacZ lacI O lacY
lacA
C E P
cAMPNo glucose
repressor CAP site entry site operator structural genes terminator
T
CA
P
pol
6.
ActivationActivationActivationActivation
DNA DNAlacZ lacI O lacY
lacA
C E P
CA
P
pol
b-galpermease
trans-acetylase
repressor CAP site entry site operator structural genes terminator
T
6.
ActivationActivationActivationActivation
DNA DNAlacZ lacI O lacY
lacA
C E P
No cAMPGlucose is present
repressor CAP site entry site operator structural genes terminator
T
6.
CA
P
pol
catabolite repression (endproduct inhibition)
ActivationActivationActivationActivation
DNA DNAlacZ lacI O lacY
lacA
C E P
CA
P Combined regulationCombined regulationpol
cAMP
glucose
lactose
rep
b-galpermease
ATP
adenylate cyclase lactose
allolactose (inductor!)
Glucose -Glucose -
Lactose +Lactose +trans-acetylase
Structure and operation of lac operonStructure and operation of lac operon
repressor CAP site entry site operator structural genes terminator
T
7.
adenylate cyclase
cyclic AMP
DNA DNA lacI O lacY
lacA
C E P
CA
P
cAMPNo glucose
lacZ
polrep
Glucose -Glucose -
Lactose +Lactose +
repressor CAP site entry site operator structural genes terminator
T
Mutant beta-galMutant beta-gal8.
DNA DNA lacI O lacY
lacA
C E P
CA
P
permease
lacZ
pol
lactose
b-gal*
Glucose -Glucose -
Lactose +Lactose +trans-acetylase
repressor CAP site entry site operator structural genes terminator
T
8. Mutant beta-galMutant beta-gal
DNA DNAlacZ lacI O lacY
lacA
C E P
CA
P
pol
rep
b-galpermease
Glucose -Glucose -
Lactose +Lactose +
repressor CAP site entry site operator structural genes terminator
T
transcription stop
stop
Transcription stop in genesTranscription stop in genes9.
DNA DNAlacZ lacI O lacY
lacA
C E P
CA
P
pol
rep
b-gal
Glucose -Glucose -
Lactose +Lactose +
repressor CAP site entry site operator structural genes terminator
T stop
Transcription stop in genesTranscription stop in genes9.
DNA DNAlacZ lacI O lacY
lacA
C E P
CA
P
pol
rep
Glucose -Glucose -
Lactose +Lactose +
repressor CAP site entry site operator structural genes terminator
T stop
Transcription stop in genesTranscription stop in genes9.
DNA DNAlacZ lacI Oc lacY
lacA
C E P
permeaseb-gal
Glucose -Glucose -
Lactose -Lactose -trans-acetylase
The operator is not able to bind the repressor
repressor CAP site entry site operator structural genes terminator
T
CA
P
polrep
pol
The Oc mutation of operonThe Oc mutation of operon10.
DNA DNAlacZ O lacY
lacA
C E P
permeaseb-gal
Glucose -Glucose -
Lactose -Lactose -trans-acetylase
The repressor is not able to bind to the operator
repressor CAP site entry site operator structural genes terminator
T lacI
CA
P
polrep
pol
The I- mutation of repressorThe I- mutation of repressor11.
DNA DNAlacZ O lacY
lacA
C E P
lacI*
Glucose -Glucose -
Lactose +Lactose +
The repressor is unable to bind lactose
repressor CAP site entry site operator structural genes terminator
T
CA
P
pol
pol
rep
The Is mutation of repressorThe Is mutation of repressor12.
DNA DNAlacZ lacI O lacY
lacA
C E P
CA
P
cAMP No glucose
CAP is unable to bind cAMP
Glucose -Glucose -
Lactose +Lactose +
repressor CAP site entry site operator structural genes terminator
T
Mutant CAP-IMutant CAP-I13.
DNA DNAlacZ lacI O lacY
lacA
C E P
cAMP
Glükóz -Glükóz -
Laktóz +Laktóz +
No glucose
repressor CAP site entry site operator structural genes terminator
T
pol
CA
P
Mutant CAP-IMutant CAP-I13.
CAP is unable to bind cAMP
DNA DNAlacZ lacI O lacY
lacA
C E P
CAP can bind promoter in the absence of cAMP
Glucose +Glucose +
Lactose +Lactose +
b-gal
trans-acetylase
rep
permease
repressor CAP site entry site operator structural genes terminator
T
CA
P
pol
pol
Mutant CAP-IIMutant CAP-II14.
Too many repressorsToo many repressors
DNA lacZ lacI O lacA
C E P
Repressor Repressor – on the plasmid– on the plasmid
repressor CAP site entry site operator structural genes terminator
DNA lacI P
Glucose -Glucose -
Lactose +Lactose +
DNAT
CA
P
polrep
rep
rep
rep
lacY
plasmid
DNA lacI P
plasmid
DNA lacI P
plasmid
DNA lacI P
plasmid
rep
rep
reprep
15.
DNA lacZ lacI O lacA
C E P
Operator Operator – on the plasmid– on the plasmid
represssor CAP site entry site operator structural genes terminator
DNA
Glucose -Glucose -
Lactose -Lactose -
DNAT
CA
P
lacY
plasmid O
DNA plasmid O
DNA plasmid O
DNA plasmid O
rep
rep
rep
b-galtrans-acetylasepermease
pol
pol
Too many Too many operatorsoperators16.
DNA DNSlacZ lacI Oc lacY-
lacA
C E P
b-gal
Glucose -Glucose -
Lactose -Lactose -
OOcc mutation mutation – on bacterial DNA– on bacterial DNA
perm*
T
rep
CA
P
pol
pol
trans-acetylase
17a. Partial diploidsPartial diploids: cis or trans-effect?: cis or trans-effect?Partial diploidsPartial diploids: cis or trans-effect?: cis or trans-effect?
DNA F plasmidlacZ- lacI O lacY
lacA
C E P
DNA DNAlacZ lacI Oc lacY-
lacA
C E P
CA
P
CA
P
polb-gal
Glucose -Glucose -
Lactose -Lactose -trans-acetylase
OOcc mutation mutation – on bacterial DNA– on bacterial DNA
permeaseb-gal*trans-acetylase
perm*
Glucose -Glucose -
Lactose +Lactose +
repressor CAP site entry site operator structural genes terminator
T
T
rep
reppol
pol
polrep
Coli lacOc lacZ+ lacY- -gal: continuously expressedF’ lacO+ lacZ- lacY+ permease: only with lactose
mutation
17b. Partial diploidsPartial diploids: cis or trans-effect?: cis or trans-effect?Partial diploidsPartial diploids: cis or trans-effect?: cis or trans-effect?
DNA lacZ lacI* O lacY-
lacA
C E P
II-- mutation mutation – on bacterial DNA– on bacterial DNA
DNA F plasmid lacZ- lacI O lacY
lacA
C E P
repGlucose -Glucose -
Lactose -Lactose -
Glucose -Glucose -
Lactose +Lactose +
b-gal
trans-acetylase
perm*
permeaseb-gal*
repressor CAP site entry site operator structural genes terminator
DNAT
T
CA
P
CA
P
polpol
rep
rep
rep
rep
rep
trans-acetylase
Coli lacI- lacO+ lacZ+ lacY- -gal with lactose
F’ lac I+ lacO+ lacZ- lacY+ permeáz with lactose
mutation
18. Partial diploidsPartial diploids: cis or trans-effect?: cis or trans-effect?Partial diploidsPartial diploids: cis or trans-effect?: cis or trans-effect?