1. REGULATION OF GENE EXPRESSION

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

3. GENE EXPRESSION IN DIFFERENT CELLS
Muscle cell
Pancreatic cells
Blood cells
Genes for
Glycolysis ON
Insulin
OFF
Glucagon
Hemoglobin
alpha cells beta cells
WBCs RBCs

4. A PROKARYOTIC AND EUKARYOTIC CELL

5. REGULATION OF GENE EXPRESSION - PROKARYOTES

6. THE OPERON Operon DNA Polycistronic mRNA Promoter Gene 1 Gene 2 Gene 3
Structural Genes 5’ 3’
AUG
UAA
UGA
UAG
Polycistronic mRNA
Protein 1
Protein 2
Protein 3

7. REPRESSORS No transcription No protein products Regulatory gene mRNA
RNA polymerase
Operator
Gene 1
Gene 2
Gene 3
Promoter 5’ 3’
No transcription
No protein products

8. REGULATORY MECHANISMS
INDUCTION
Repressor is INACTIVATED through inducers to INITIATE / INDUCE transcription
REPRESSION
Repressor is ACTIVATED through corepressors to PREVENT / REPRESS transcription

9. INDUCTION Active repressor No transcription, translation Inducer
Inactive repressor

10. REPRESSION Inactive repressor Transcription Translation Corepressors
No transcription, translation

11. GENE REGULATION IN EUKARYOTES

12. Gene Regulation Can Take Place at Many Levels
Chromosome
Transcription
Processing of transcripts
Translation

13. GENE REGULATION AT THE CHROMOSOMAL LEVEL

14. Two Types of Chromatin HETEROCHROMATIN Trancriptionally inactive
tightly condensed
EUCHROMATIN
Transcriptionally active
Relatively relaxed

15. CHROMATIN STRUCTURE

16. EFFECT OF CHROMATIN STRUCTURE ON TRANSCRIPTION
Control region outside nucleosome
Control region within nucleosome
GENE IS INACTIVE
GENE IS ACTIVE

17. Histone Acetylation
HAT

18. Histone Acetylation

19. DNA Methylation

21. X-Inactivation Inactive X-Chromosome (Barr body) Underacetylated at H4
Hypermethylated

22. 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

23. Arrangement of DNA

25. Antibody Diversity 1200 x 24,000 = 28,800,000 antibody molecules
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

26. Mobile Genetic Elements - Transposons

27. REGULATION AT THE LEVEL OF TRANSCRIPTION

28. 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

29. 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

30. Enhancers/Silencers

31. 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

32. cAMP Response Element (CRE)
5’- TGACGTCA -3’
3’- ACTGCAGT -5’

33. cAMP Response Element (CRE)
cAMP – second messenger of several hormones (glucagon, epinephrine)
cAMP  = protein kinase A 
protein kinase A phosphorylates the cAMP RESPONSE ELEMENT BINDING PROTEIN (CREB)
Phosphorylated CREB binds to the CRE binding protein (CBP)
CBP connects CREB to the basal transcription machinery and promotes gene activation

34. 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

35. Activation of CREB

36. Glucocorticoid Response Element

37. GENE REGULATION BY PROCESSING OF TRANSCRIPTS

38. Alternative Splicing

39. RNA EDITING

40. Regulation of Translation by Phosphorylation

41. mRNA Stability

42. Regulation of Transferrin Expression

43. Regulation of ferritin expression

44. RNA Interference
…will be done with therapeutics

45. The End!