fine control of prokaryotic transcription; lactose...
TRANSCRIPT
Gene Regulation- I
Fine Control of Prokaryotic Transcription;
Lactose operon
By Professor MinDong Song, Ph.D
Division of Life Science,
Konkuk University, Chungju, Korea
Gene Expression
Introduction
DNA
mRNA
Protein
4.6 x 106 bp
(4,639,221bp)
Average size of
gene ≈ 1.1 x 103 bp
Ca. 4180
(4,377 genes )
4,290 proteins
E.coli
Housekeeping proteins…
Luxury, Auxiliary proteins… 4,290 of these genes encode proteins; the rest RNAs
Contents
Lactose Operon ; lac operon
Galactose Operon ; gal operon
Arabinose Operon ; ara operon
Tryptophan Operon ; trp operon
Types of Gene Regulation
1. Negative Regulation : Repressor
2. Positive Regulation : Activator
- Induction : catabolism
- Repression : anabolism
Lactose operon model
- In 1961, Francois Jacob and Jacques Monod
Lactose operon
• Gene transcription can be switched on and off by gene regulation proteins.
• The lac operon in E. coli is an example of that dual control.
• Glucose and lactose levels control the initiation of transcription of the lac operon, i.e. whether the lac operon is switched "ON" or "OFF".
Bacterial Growth curve
Bacterial Growth curve
Two-step Growth curve
glucose + lactose: glucose is used first then lactose; note internal lag
Enzyme Activity
What is operon?
Operon[=operate + -on]
• Transcription unit[전사단위]
- The unit of regulation [전사조절단위]
- consists of several structural cistrons all regulated together
[2개 이상의 구조유전자가 하나의 조절자에 의해 일률적으로 조절 받
는 전사단위]
- Also possesses regulatory elements [조절자를 지니고 있음]
P
P
Lac operon map
z y a i o p pi
CAP
Structural genes Regulatory
sites
β-galactosidase
Lactose permease
Galactoside transacetylase Repressor
CAP: catabolite activator protein
P : promoter(RNA polymerase binding site)
O: operator(Repressor binding site) Lac Operon
Complementary test system for
Isolation of Mutants in E.coli
E. coli chromosome
F’ plasmid
Partial
Diploids
Mutants
Lac- Mutants-I ;
unable to use lactose as a carbon source
Lac- Mutants
1) F’lac- / lac+
2) F’ lac+/ lac-
Lac+
Lac- Mutants
F’ lac-/ lac-
β-galactosidase
Lac+
Lac-
called
lac Z, lac Y
F’y-z+/y+z-
F’y+z-/y-z+
F’y-z+/y-z+
F’y+z-/y+z-
Lac+
Lac-
Lac- Mutants-II
F’y-z+/y-z+
(y- cell)
[14C]lactose
Experiments with
[14C]lactose
Cannot enter
y- cell
Y gene is
permease
uptake
z- cell
Z gene is
galactosidase
F’y+z-/y+z-
(z- cell)
Is the Lactose Real Inducer ?
Lactose -- beta-galactosidase- Glucose + Galactose
Lactose -- beta-galactosidase- Allo-lactose
(real inducer)
Positive control of the lac operon
No Glucose
→ increase cAMP conc.
→cAMP binds to CRP(or CAP)
→ cAMP•CRP complex
→ enhance RNA polymerase to Promoter
→ Increase Transcription
Negative Regulation by Repressor in lac operon
Pi i z P a y 유도물질(inducer)이 없을 때
억제유전자 mRNA
억제 단백질
억제 단백질(repressor)이 operator에
결합하여 RNA중합효소가 operon의
전사를 방해한다
Pi i z P a y 유도물질(inducer)이 있을 때
억제유전자 mRNA
억제 단백질
O
Allo-lactose (불활성화 억제 단백질)
베타-갈락토오스 분해효소
락토오스 침투효소
아세틸 전이 효소
CAP lac a lac y O lac z P
RNA 중합효소
CAP 글루코오스
농도가 낮을 때
베타-갈락토오스 분해효소
락토오스 침투효소
아세틸 전이 효소
mRNA
+
ribosome
Promoter 결합
Positive Regulation by CAP in lac operon
Summary of lac operon
1. Negative Regulation by Repressor
1-1. In the absence of inducer(lactose)
→ turn off lac operon by repressor
1-2. In the presence of inducer
→ turn on lac operon by inducer-repressor
2. Positive Regulation by Activator
No Glucose → increase cAMP conc. →cAMP binds to CRP(or CAP)
→ cAMP•CRP complex → enhance RNA polymerase to Promoter →
Increase Transcription
Animation for lac operon
• Animation for lac operon
참고문헌 및 web sites
1. Molecular Biology-Genes to Proteins,(4th ed.), BE Tropp, Jones & Bartlett(2012)
2. GENES X, Krebs et al., Jones & Bartlett(2011)
3. Molecular Biology(4th ed.), RF Weaver, McGraw Hill(2008)
4. Molecular Biology of the gene(6th ed.), Watson et al, CSH Press(2008) 5. Essential GENES(2nd ed.), Krebs et al ., Jones & Bartlett(2010) 6. 분자생물학 입문, 대표역자 송민동 , ㈜월드사이언스(2011)
NEXT Lecture
Gene Regulation –II
Fine Control of Prokaryotic Transcription
• Galactose operon
• Arabinose operon
• Tryptophan operon