Chapter 6
Regulation of Prokaryotic Gene Expression
6.1 Overview
1. What are Gene Expression and
Regulation?
(1) Gene expression

Constitutive Expression

Regulated/Adaptive Expression
(2) Gene regulation/control
2. Influencing factors
 Nutritional status
 Environmental factors
 Hormone level
 Developmental stage
3. Operon
(1) What is an operon?
(2) Operon types
 Inducible operon
 Repressible operon
(3) Gene regulation of operon
 Negative regulation
 Positive regulation
负控诱导系统
正控诱导系统
正控阻遏系统
负控阻遏系统
6.2 The Regulation of lac Operon
1. Organization of lac operon
Regulatory gene
Structural Genes
lacI
PlacI
lacZ
lacY
lacA
DNA
Plac Olac
mRNA
Protein
repressor
β -Galactosidase
Permease
Transacetylase
3. Positive control of lac operon
cAMP
CAP (catabolite activator protein)
or cAMP receptor protein (CRP)
4. Negative contral of lac operon
1. + Inducer
Repressor cannot bind
(lactose/
allolactose)
p
t
lacI
transcripts
Induced
p
o
Repressor
t
lacZ
-galactosidase
lacY
Permease
lacA
Transacetylase
2. No Inducer
p
Repressor binds to laco
lacI
transcript
Animation
lacZ
o
Repressed
lacY
lacA
t
6.3 The Regulation of trp Operon
1. Organization of trp operon
2. The Repression of trp Operon
trpR → Repressor
Corepressor
3. The Attenuation Mechanism of trp Operon
 Attenuator
 Mechanism of Attenuation
When Ribosome reaches Trp codon
 Trp is scarce
 Trp is aboudant
Attenuation model in Trp starved cells.
Attenuation model in Trp non-starved cells
Animation
5. Generality of Attenuation
6.4 The Regulation of Other Operons
1. The Regulation of ara Operon
(1) organization
P
t
araC
Activator/
Repressor
t
CRP
O2
AraC dimer
P
O1
I1 I2
araB
araA
araD
Arabinose absent →Negative control
O2
araC
araB
A
D
O1 CRP araI
PC
PBAD
Blocked
Arabinose present → Positive control
O2
araC
araB
A
D
O1 CRP araI
PC
PBAD
Transcription
2. The Regulation of rRNA Operon
(1) organization
6.5
Riboswitches
1. What is a riboswitch?
Riboswitches have two important domains:
 an aptamer
 an expression platform
2. Mechanism of Riboswitches
(1) Inhibition of Translation Initiation
(2) Transcription termination
(3) Auto-cleavage
3. Tempting Targets
4. Riboswitches and the RNA World hypothesis
5. Riboswitches as Antibiotic Targets
Brantl, S.
Bacterial gene regulation: from transcription attenuation to
riboswitches and ribozymes.
Trends Microbiol, 2004, 12:473-475.
Mandal, M. and R. R. Breaker.
Gene Regulation by Riboswitches.
Nat Rev Mol Cell Biol, 2004, 5:451-463.
Blount KF, Breaker RR.
Riboswitches as antibacterial drug targets".
Nat Biotechnol, 2006, 24 (12): 1558-64.
6.6 Time Regulation
1. Time Regulation of Sigma Factors
Different sigma factors recognize different
promoters and thus, the availability of sigma
factors can regulate the transcription of genes
associated with these promoters.
Early
Middle
Late
2. Time Regulation of λ phage
 Uncommitted.
 Committed.
Lysogeny
Lysis
 Execution
Lysogeny
Lysis
6.7 Post-Transcriptional Regulation
1. Translation Initiation of Regulation
(1) Ribosome binding site (rbs)
(2) SD sequencing
(3) mRNA secondary structure
(4) Initiational codon
2. Regulation of Rare Codon
3. Transcriptional Regulation of Overlapping Gene
4. Translational Repression
Summary
1. Concepts
Gene Expression
Operon
Constitutive Expression Inducible Operon
Regulated Expression
Gene Regulation
Attenuator
Attenuation
Repressible Operon Riboswitch
2. Differences between inducible operon and repressible operon
3. The regulation mechanism of lac operon
4. The regulation mechanism of trp operon (attenuation)
5. The regulation mechanism of ara operon
6. The regulation mechanism of riboswitches