Transcript REGULATION OF GENE EXPRESSION IN EUKARYOTES

REGULATION OF GENE
EXPRESSION
WHY REGULATE GENE
EXPRESSION??
 Adaptation
(Energy Conservation)
 Development and differentiation
GENE EXPRESSION IN DIFFERENT CELLS
Genes for
Muscle cell
Pancreatic cells
alpha cells beta cells
Blood cells
WBCs
RBCs
Glycolysis
ON
ON
ON
ON
ON
Insulin
OFF
OFF
ON
OFF
OFF
Glucagon
OFF
ON
OFF
OFF
OFF
Hemoglobin
OFF
OFF
OFF
OFF
ON
A PROKARYOTIC AND
EUKARYOTIC CELL
REGULATION OF GENE
EXPRESSION PROKARYOTES
THE OPERON
Operon
DNA
Structural Genes
5’
Promoter
Polycistronic
mRNA
Gene 2
Gene 1
AUG
UAA AUG
Protein 1
Gene 3
UGA AUG
Protein 2
3’
UAG
Protein 3
REPRESSORS
Regulatory gene
mRNA
Repressor
RNA polymerase
Operator
5’
Promoter
Gene 1
Gene 2
Gene 3
3’
No transcription
No protein products
REGULATORY MECHANISMS
INDUCTION
Repressor is INACTIVATED through
inducers to INITIATE / INDUCE
transcription
REPRESSION
Repressor is ACTIVATED through
corepressors to PREVENT / REPRESS
transcription
INDUCTION
Active repressor
No transcription, translation
Inducer
Transcription
Translation
Inactive
repressor
REPRESSION
Inactive repressor
Transcription
Translation
Corepressors
Active repressor
No transcription, translation
GENE REGULATION IN
EUKARYOTES
Gene Regulation Can Take
Place at Many Levels
 Chromosome
 Transcription
 Processing of transcripts
 Translation
GENE REGULATION AT THE
CHROMOSOMAL LEVEL
Two Types of Chromatin
• HETEROCHROMATIN
Trancriptionally inactive
tightly condensed
• EUCHROMATIN
Transcriptionally active
Relatively relaxed
CHROMATIN
STRUCTURE
EFFECT OF CHROMATIN
STRUCTURE ON TRANSCRIPTION
Control region outside
within
nucleosome
nucleosome
GENE
GENEISISINACTIVE
ACTIVE
Histone Acetylation
HAT
Histone Acetylation
DNA Methylation
X-Inactivation
• Inactive X-Chromosome (Barr body)
– Underacetylated at H4
– Hypermethylated
X-inactivation in humans
• Red-green color blindness
– Males = fully color blind
– Females = mosaic retinas
• Anhidrotic ectodermal dysplasia
– Males = absence of teeth, lack of sweat
glands
– Females = random patterns of tissue with or
without sweat glands
Arrangement of DNA
Antibody Diversity
• Light chains:
– Up to 300 Variable, 4 Joining and 1 Constant
region
• 300 x 4 = 1, 200 light chains
• Heavy chains:
– Up to 500 Variable, 4 Joining and 12 Diversity
regions and 12 constant regions
• 500 x 4 x 12 = 24, 000 light chains
1200 x 24,000 = 28,800,000 antibody
molecules
REGULATION AT THE LEVEL
OF TRANSCRIPTION
• GTFs only produce a basal level of
transcription i.e. very low
• Gene-specific factors (activators) are
further required to regulate the activity
of gene expression
Enhancers/Silencers
• Upstream or downstream
• Close to the promoter or thousands of base
pairs away
• On either of the two strands of DNA
• Act through intermediary or gene specific
transcription factors proteins
• Enhancers activate transcription
• Silencers deactivate transcription
Enhancers/Silencers
Response Elements
• Enhancers contain response elements
that are responsive to certain metabolic
factors
–Cyclic AMP response element (CRE)
–Glucocorticoid response element (GRE)
–Heat shock element (HSE)
• REs bind transcription factors produced
under certain cell conditions to activate
several related genes
cAMP Response Element (CRE)
5’- TGACGTCA -3’
3’- ACTGCAGT -5’
CREB – the most important protein
that you have never heard of
• Implicated in
– Cell proliferation
– Cell differentiation
– Spermatogenesis
– Release of somatostatin (inhibitor growth hormone)
– Development of T lymphocytes
– Metabolism of the pineal gland
– Adaptation to physical stress
– Transcription of metabolic enzymes
– Critical in learning and long term memory
Activation
of CREB
Glucocorticoid Response Element
GENE REGULATION BY
PROCESSING OF
TRANSCRIPTS
Alternative Splicing
RNA EDITING
Regulation of Translation by
Phosphorylation
mRNA
Stability
Regulation of Transferrin
Expression
Regulation of ferritin
expression
RNA Interference
…will be done with therapeutics
The End!