1. Regulation of Gene Expression
Emphasizing Hormonal Action
Presented by: Sony Peter
Lecturer
Department of Biochemistry
Goba College of Medicine and Health
Sciences
Madawalabu University

2. Classification of gene with respect to their
Expression:
• Constitutive ( house keeping) genes:
• 1- Are expressed at a fixed rate, irrespective to the cell
condition.
• 2- Their structure is simpler
• Controllable genes:
• 1- Are expressed only as needed. Their amount may
increase or decrease with respect to their basal level in
different condition.
• 2- Their structure is relatively complicated with some
response elements

3. • Several steps in the gene expression process
may be modulated, including the
• 1.transcription,
• 2. RNA splicing
• 3.translation, and
• 4.post-translational modification of a protein.

4. • Process of alteration of gene expression been
studied has been studied in in detail &
involves modulation of gene transcription.
Transcription control can result in tissue
specific gene expression& influenced by
hormones, heavy metals etc.
In simple terms, regulation of gene expression
is of two types
1.positive regulation.
2.negative regulation.

5. 1. Positive Rregulation:
When the expression of genetic information is
quantitatively increased by the presence of
specific regulatory element, it is known as
positive regulation.
Elements or molecules modulating positive
regulation is known as positive regulator.

7. 2.Negative Regulation.
When the expression of genetic information is
diminished by the presence of specific
regulatory element, it is called the negative
regulation.
The element or molecule mediating the
negative regulation is called a negative
regulator.

9. Human gene regulation occur at
several levels
1. Regulation at the level of DNA
2. Transcriptional control
3. RNA Processing control
4. RNA transport and localization control
5. Translation control
6. mRNA degradation control
7. Protein activity control

10. Human gene regulation occur at
several levels

11. 1. Regulation at the level
of DNA
The effect of chromosome
structure on gene
regulation.
DNA is wrapped tightly
around histone proteins to
form nucleosome.

12. Promoter blocking by nucleosome
• Histones positioned over promoter block the
assembly of transcription factor complexes.

13. DNA Methylation
• Methylation of DNA was once thought to play a
major role in gene regulation.
• Many inactive human genes are methylated.
• Methylation is now viewed as having a less direct
role, blocking accidental transcription of “Turned
Off Genes”.
• Methylation results in a human disease called fragile X
syndrome; FMR-1 gene is silenced by methylation.

14. 2. Transcriptional Control
Regulating Promoter Access
One way to control transcription is to regulate
the initiation of transcription.
Protein- binding nucleotide sequences on the
DNA regulate the initiation of transcription by
modulating the ability of RNA polymerase to
bind to the promoter.

15. Binding the protein to the regulatory sequence
either blocks transcription by getting in the way of
RNA polymerase, or stimulate transcription by
facilitating the binding of RNA polymerase to the
Promoter

16. Transcription control in Prokaryotes
Significance:
In Bacteria, the primary function of gene control is
to adjust the cell’s activities to its immediate
environment.
Changes in gene expression alter which enzymes
are present in the cell in response to the quantity
and type of available nutrients and the amount of
Oxygen present.
Almost all of these changes are fully reversible,
allowing the cell to adjust its enzyme levels up or
down as the environment changes.

17. Transcriptional Control in Eukaryotes
• In human, with relatively constant internal
environment, the primary function of gene
control in a cell is not to respond to that cell’s
immediate environment, but rather to
participate in regulating the body as a whole.
• Transcription control, more common, is
effected by binding of protein to regulatory
sequences within the DNA.

18. Regulatory proteins read DNA without
unwinding it.
• Within the major groove, the nucleotides
hydrophobic methyl groups, hydrogen atoms and
hydrogen bond donors and acceptors protrude.
• The pattern created by these chemical groups is
unique for each of the four possible base-pair
arrangement, providing a ready way for a protein
nestled in the groove to read the sequence of
base

19. Major groove and Minor groove of DNA
CH3- Hydrophobic methyl group
Yellow color- Hydrogen bond donors
Red color- Hydrogen bond acceptors
Blue color- Hydrogen atoms unable to form hydrogen bonds

20. DNA Binding Motifs
• DNA binding motif on the protein chain
permit it to interlock with the major groove of
the DNA helix.
• 1. The Helix-Turn-Helix motif
• 2. Homeodomain motif
• 3. The Zinc Finger motif
• 4. The Leucine Zipper motif

21. 1. The Helix-Turn-Helix motif
This motif is constructed from two alpha-helical
segments of the protein linked by a short non
helical segment, the turn.
This motif has been identified in hundreds of
DNA- binding proteins.

22. 2. Homeodomain motif
It is a special class of Helix-Turn-Helix motif.
More than 50 of these regulatory proteins have
been analyzed and they all contain a nearly
identical sequence of 60 amino acids, the
homeodomain.

23. 3. The Zinc Finger motif
• This uses one or more zinc atoms to
coordinate its binding to DNA called zinc
fingers.
• The more zinc fingers in the cluster, the
stronger the protein binds to the DNA.

24. 4. The Leucine Zipper motif
• Here two different protein subunits cooperate
to create a single DNA binding site.
• This motif is created where a region on one of
the subunits containing several hydrophobic
amino acids (usually Leucine) interacts with a
similar regions on the other subunit.

25. The DNA Binding motifs

26. Transcriptional control in humans
operates at a distance
• In human, many genes must interact with one
another.
• Many regulatory sequences scattered around
the chromosome can influence a particular
gene’s transcription

28. The transcription complex that
positions RNA polymerase at the
beginning of a gene consists of 4
kinds of proteins.
• Basal factors
• Co-activators
• Activators
• Repressor

29. Human transcription complex

30. RNA Processing
Processing of the primary transcript
This include excision of introns, capping of 5’ end and addition of
Polyadenylate tail to 3’ end of the primary transcript.
1. Exons and Introns- Introns removed by RNA Processing or RNA Splicing
Small nuclear ribonucleoprotein (snRNPs) play a role in RNA splicing.
These particles reside in the nucleus and composed of proteins and a special
type of RNA called small nuclear RNA (snRNA).
Multiple snRNPs base pair with introns to form a larger complex called
Spliceosome. The introns loops out and is exised.

31. How spliceosomes process RNA

32. RNA processing cont.…….
RNA splicing provides a potential point where the expression of a gene can be
controlled, because exons can be spliced together in different ways, allowing
a variety of different polypeptides to be assembled from the same gene.
In many cases, gene expression is regulated by changing which splicing event
occur during different stages of development or in different tissues.
Example, The alternative splicing in action found in thyroid and
hypothalamus.
Thyroid produce Calcitonin
Hypothalamus produce CGRP (Calcitonin gene related peptide) as a part of
their function.
Different purpose, but the hormones are made using the same transcript.

33. RNA processing cont.…….

35. RNA processing cont.…….
• 7-methylguanine capping at 5’ end
This capping at 5’ end of the transcript is appended by
nucleoside phosphohydrolase, guanyltransferase and
guanine methylferase.
• 3’polyadenylation
After the 5’ capping, the 3’ end of the transcript will be
added by a long poly A tail, consisting of a string of
about 20-200 adenine ribonucleotides byMg2+
dependent nucleoplasmic poly-A polymerase.

36. RNA transport and localization control
Processed mRNA transcript exit the nucleus through nuclear pores.
Its active process.
Transcript has to be recognized by the receptors lining the interior of the
pore.
Poly A tail play a role in this recognition

37. Translation control
• The translation of processed mRNA transcript by the ribosomes in the
cytoplasm involves a complex of proteins called Translation factors.
• In some cases, gene expression is regulated by modification of one or
more of these factors.
• In other instances, Translation repressor proteins shut down translation by
binding to the beginning of the transcript, so that it cannot attach to the
ribosome.
• Example, the production of ferritin is normally shut off by a translation
repressor protein called aconitase.

38. mRNA degradation control
• Another aspect that affects gene expression is the stability of mRNA
transcripts in the cell cytoplasm.
• Human mRNA transcripts are very stable compared to lower organisms.
• Example, beta-globin gene transcript have a half-life of over 10 hrs.
However, the transcripts encoding regulatory proteins and growth factors are
usually much less stable, with a half-life < 1 hr.
WHAT MAKES THESE PARTICULAR TRANSCRIPTS SO UNSTABLE?
- A sequence of A and U nucleotides near 3’ end
- Destabilize and prone to enzyme attack
- Some mRNA transcripts digested by endonucleases.

39. mRNA degradation control con……
Example, Histone transcripts have a half-life of about 1 hr in the cells that are
actively synthesizing DNA, at other times during cell cycle, the poly A tail is
lost and the transcripts are degraded within minutes.
• Some hormones which enhance the production of proteins also
increase the half life of the protein’s mRNA.
Estrogen : t1/2 from 2- 5hr to >24hr
Prolactin : t1/2 from 5 hr to 92hr
The short half-lives of the mRNA transcripts of many regulatory genes are
critical to the function of those genes, as they enable the levels of regulatory
proteins in the cell to be altered rapidly.

40. Protein activity control
• Inteins are the protein analogs of self-splicing RNA introns, as they post-
translationally excise themselves from a variety of protein hosts. Intein
insertion abolishes, in general, the activity of its host protein, which is
subsequently restored upon intein excision.
• Proteins builded after translation can be
• • functional or
• have to undergo a maturation process (exo/-
endopeptidation)
or functional group addition by phosphorylation, acetylation,
methylation … to functional.

41. Hormonal control of gene expression
Hormones are molecules that are produced in one cellular location in the
human body and whose effects are seen in another tissue or cell type.
Hormones can be proteins or steroids
Eg, insulin, epinephrine estrogen, progesterone, testosterone control gene
expression.
The protein hormones do not enter the cell, but bind to receptors in the cell
membrane and mediate gene expression through intermediate molecules.
The steroid hormones enter the cell and interact with steroid receptor
proteins to control gene expression.

42. Peptide hormone action

44. Peptide hormone action con…..
Hormones are synthesized in various specialized secretory cells (endocrine
cells) and are released into blood stream.
The peptide hormones do not normally enter the cells because of their
relative large size. Their effect is mediated by receptor proteins located in
target cell membranes and by the intracellular level of cAMP (called the
secondary messenger).
The cAMP activates a protein kinase (A- Kinase) which phosphorylates
(activates) many specific enzymes.

45. Steroid hormone action

46. Steroid hormone action con…….
Steroid hormones are small molecules that readily enter cells through plasma
membrane.
Once inside the appropriate target cells, the steroid hormones become tightly
bound to specific receptor proteins which are present only in the cytoplasm
of target cells.
The hormone-receptor protein complex activate the transcription of specific
genes according to following two methods:
1. The H-R PC interact with specific non-histone chromosome proteins and
this interaction stimulates the transcription of correct genes.
2. H-R PC activate transcription of target genes by binding to specific DNA
sequences present in the cis-acting regulatory regions of the genes.
In both of these cases, the H-R PC would function as positive regulators or
activators of transcription.

47. Steroid hormone action con…….
Glucocorticoid hormones influence nutrient metabolism in most of the body
cells by promoting the metabolism of glucose, proteins and fats.
The effect of glucocorticoids is to activate the transcription of specific genes.
The hormone is released from the endocrine cells and secreted into the blood
stream when the individual is fasting and needs to regulate its blood levels of
glucose, a.a- and fats.
The hormone molecules diffuse across the plasma membrane of target cells
and bind to glucocorticoid receptors.

48. Steroid hormone action con…….

49. Steroid hormone action con…….
The thyroid hormones tri iodo thyronine and tetra iodo thyronine, T3 and T4
have marked effect on the growth, development and metabolic function of
virtually all organ systems and tissues of human body.
A significant amount of T3 is derived from T4 by 5’ deiodinase in various
tissues.
Because of the marked alteration in the rate of oxygen consumption
identified in hypothyroidism and hyperthyroidism, initial studies on
mechanism of action of the thyroid hormones focused on mitochondrial
function.
Experimental works shows that T-H administration increased the rate of RNA
synthesis, specially stimulating the accumulation of mRNAs which codes for
specific proteins.

50. Steroid hormone action con…….
The following T-H depended effects have also been analyzed:
1. Stimulation and regulation of growth hormone gene expression
2. Stimulation of malic enzyme mRNA in the liver
3. Stimulation of several other genes that encode hepatic proteins of
unknown function.
4. Stimulation of the alpha-myosin heavy chain gene in the myocardium.
5. Inhibition of thyrotrophin and the beta-myosin heavy chain gene.