REGULATION OF GENE EXPRESSION. WHY REGULATE GENE EXPRESSION?? Adaptation (Energy Conservation) Development and differentiation.

REGULATION OF GENE REGULATION OF GENE EXPRESSIONEXPRESSION

WHY REGULATE GENE EXPRESSION??

Adaptation

(Energy Conservation) Development and differentiation

GENE EXPRESSION IN DIFFERENT CELLS

Muscle cell Pancreatic cells alpha cells beta cells

Blood cellsWBCs RBCsGenes for

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 A PROKARYOTIC AND EUKARYOTIC CELLEUKARYOTIC CELL

REGULATION OF GENE REGULATION OF GENE EXPRESSION - EXPRESSION - PROKARYOTESPROKARYOTES

THE OPERONTHE OPERON

DNA

Promoter Gene 1 Gene 2 Gene 3

Structural Genes

5’ 3’

AUG AUG AUGUAA UGA UAGPolycistronic mRNA

Protein 1 Protein 2 Protein 3

Operon

REPRESSORSREPRESSORS

3’

mRNA

Promoter Gene 1 Gene 2 Gene 35’

Operator

No transcription

No protein products

Regulatory gene

RepressorRNA polymerase

REGULATORY MECHANISMSREGULATORY MECHANISMS

INDUCTIONRepressor is INACTIVATED through inducers to INITIATE / INDUCE transcription REPRESSION

Repressor is ACTIVATED through corepressors to PREVENT / REPRESS transcription

INDUCTIONINDUCTION

Inducer

Inactive repressor

Active repressor

No transcription, translation

Transcription

Translation

REPRESSIONREPRESSIONInactive repressor

Corepressors

Transcription

Translation

No transcription, translation

Active repressor

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 Two Types of Chromatin

• HETEROCHROMATIN Trancriptionally inactive

tightly condensed

• EUCHROMATIN

Transcriptionally active

Relatively relaxed

CHROMATIN CHROMATIN STRUCTURESTRUCTURE

EFFECT OF CHROMATIN STRUCTURE ON TRANSCRIPTION

Control region outside nucleosome

GENE IS ACTIVE

Control region within nucleosome

GENE IS INACTIVE

Histone AcetylationHistone Acetylation

HAT

Histone AcetylationHistone Acetylation

DNA MethylationDNA Methylation

X-InactivationX-Inactivation

• Inactive X-Chromosome (Barr body)– Underacetylated at H4– Hypermethylated

X-inactivation in humansX-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)cAMP Response Element (CRE)

5’- TGACGTCA -3’

3’- ACTGCAGT -5’

CREB – the most important protein CREB – the most important protein that you have never heard ofthat 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 Glucocorticoid Response Element

GENE REGULATION BY PROCESSING OF TRANSCRIPTS

Alternative Splicing

RNA EDITING

Regulation of Translation byRegulation of Translation byPhosphorylationPhosphorylation

mRNA mRNA StabilityStability

Regulation of Transferrin Regulation of Transferrin ExpressionExpression

Regulation of ferritin Regulation of ferritin expressionexpression

RNA Interference

…will be done with therapeutics

The End!