Eukaryotic regulation

1. GENETIC REGULATION IN
EULARYOTES

2. LEVELS
1.Level of transcription
Trans-acting molecules
Cis-acting elements
2. Posttranscriptional level
Alternative mRNA splicing
Control of mRNA stability
Control of mRNA editing
3. DNA level
Access to DNA
Amount of DNA
Arrangment of DNA
Mobile DNA elements
.

3. I.LEVEL OF TRANSCRIPTION
TRANS ACTING MOLECULES
Specific transcription factors(STF)
• Two binding domains:
1. The DNA-binding domain
• contains specific structural motifs, such as zinc fingers
that bind sequences in DNA.
2. The transcription-activation domain recruits the
general transcription factors ([GTFs]
• These facilitate formation of the transcription initiation
complex (RNA polymerase II plus the GTFs) at the
promoter, and, thus, activate transcription

5. CIS ACTING ELEMENTS
• The area on DNA where the DNA binding
domain of the specific transcription factors
binds
• Eg, Hormone-Response Elements (HREs) are
cis-acting DNA sequences that bind trans-
acting protein factors and regulate gene
expression in response to hormonal signals.

7. INTRACELLULAR RECEPTOR
• Steroid hormone (glucocorticoids,
mineralocorticoids, androgens, and
estrogens), vitamin D, retinoic acid, and
thyroid hormone receptors
• DNA-binding domain
• Activation domain
• Ligand-binding domain.

8. STEPS
• Cortisol bind to soluble, intracellular receptors at the
ligand-binding domain.
• Binding causes a conformational change in the
receptor that activates it.
• The receptor–ligand complex enters the nucleus,
dimerizes
• Binds via a zinc finger motif to nuclear DNA at a cis-
acting regulatory element, the glucocorticoid-response
element (GRE).
• Binding allows recruitement of coactivators to the
activation domain and results in increased expression
of cortisol-responsive genes

9. Intracellular receptor

10. CELL SURFACE RECEPTOR
• Insulin, epinephrine, and glucagon.
STEPS:
• Hormone binds its G protein–coupled plasma membrane
receptor
• Increased intracellular cAMP
• Protein kinase A–mediated phosphorylation
• A trans-acting factor (cAMP response element–binding
[CREB] protein) is phosphorylated and activated.
• Active CREB protein binds via a leucine zipper motif to a cis-
acting regulatory element, the cAMP response element
(CRE)
• Transcription of target genes with CREs in their promoters.

11. Cell surface receptor

12. II. Regulation by processing of
messenger RNA
1. Splice site choice
2. mRNA editing
3. mRNA stability

13. 1.Splice site choice
Tissue-specific protein isoforms can be made
from the same pre-mRNA through differential
use of alternative splice sites
eg.Tropomysin

14. Alternative splicing

15. mRNA editing
• A base in the mRNA is altered
• Example:
• Apo B mRNA is made in the liver and the small
intestine.
• In the intestine only, the C residue in the CAA codon for
glutamine is deaminated to U, changing the sense
codon to a nonsense or stop codon
• This results in a shorter protein (apo B-48) being made
in the intestine (and incorporated into chylomicrons)
• The one made in the liver (apo B-100, full-length,
incorporated into VLDL).

16. mRNA editing

17. mRNA stability
• How long an mRNA remains in the cytosol
before it is degraded influences how much
protein product can be produced from it.
• Eg Iron metabolism

18. mRNA stability

19. TRANSLATION OF mRNA
• phosphorylation by kinases of the eukaryotic
translation initiation factor, eIF-2
• This inhibits its function and so inhibits
translation at the initiation step

20. III.Regulation through modifications
to DNA
• Access to DNA
• Amount of DNA
• Arrangment of DNA
• Mobile DNA elements

21. 1.ACCESS TO DNA
• DNA is found complexed with histone and
nonhistone proteins to form chromatin
ACTIVE DNA (euchromatin):
• Acetylation (HAT)
• Phosphorylation
• Hypomethylation
• Nucleosome repositioned(chromatin
remodeling)

22. 2.AMOUNT OF DNA
• A change up or down in the number of copies
of a gene can affect the amount of gene
product produced.
• An increase in copy number (gene
amplification) has contributed to increased
genomic complexity
• Seen in diseases and with MTX

23. 3.DNA REARRANGEMENTS
Fig. DNA rearrangements in the generation of immunoglobulins.
V= variable; D = diversity; J = joining

24. 4.MOBILE DNA
• Transposons (Tns) are mobile segments of DNA that move
in an essentially random manner from one site to another
on the same or a different chromosome.
• Movement is mediated by transposase, an enzyme
encoded by the Tn itself.
• Movement can be :
Direct, in which transposase cuts out and then inserts the
Tn at a new site
Replicative, in which the Tn is copied and the copy
inserted elsewhere while the original remains in place.
• Replicative transposition frequently involves an RNA
intermediate, in which case the Tn is called a
retrotransposon .
• Can alter gene expression and even to cause disease
• Eg, hemophilia, duchene dystrophy

25. DIRECT MOVEMENT

26. REPLICATIVE MOVEMENT