DLA 24: Gene Regulation Flashcards
What are the effects of an activator binding to an enhancer sequence?
- It stabilizes the basal transcription apparatus (RNA polymerase/general transcription factors)
- Increases transcription levels
Three modes of action
1) Competition:
- Activator and repressor compete to bind to enhancer region
- If repressor binds, activator can’t = reduces transcription
2) Quenching
- Repressor protein binds to DNA binding domain of activator protein, preventing activator protein from binding to DNA site = reducing transcription
3) Blocking
- Repressor protein binds to the activation domain of of an activator protein = prevents activator protein from interacting w the basal transcriptional machinery = reduced transcription (Activator protein still still binds, but isn’t functional)
Hypoxia Response
- Reduction in the normal level of tissue oxygen tension
- HIF-1 = up-regulation of genes
- HIFI-Alpha and HIFI-Beta transcription factor:
- must be dimerize
- Bind to a specific DNA sequence = Hypoxia Response Element (HRE) 5’-TACGTG-3’
(HIF-1) Hypoxia-Inducible Transcription Factor
Structure
-Regulates gene response to low oxygen
- HIF-1-Alpha Inducible = O2 sensitive
- HIF-1-Beta = constitutive
- Similar: Dimerization and DNA binding domain
- Differ: Transactivation domain
HIF-1 Regulation
Oxygen
- Generated by activity of Prolyl Hydroxylase
- High oxygen: HIF-1-Alpha = hydroxylated and degraded by proteosome (Ubiquitin ligase)
- Low/no oxygen: HIF-1-Alpha stabilized, dimerizes w HIF-1-Beta to activate multiple genes that enhance oxygen delivery to tissue and/or energy supply
Glucocorticoids/hormone response element
- Steroids, small, hydrophobic
- Mediated by glucocorticoid receptor (GR)
- Zinc-finger type Transcription Factor
- Key anti-inflammatory treatment
Mediation by Glucocorticoid receptor (GR)
GR = inactive w/o glucocorticoid = held in cytoplasm
Glucocorticoid + GR bind = dissociation from regulatory complex = GR dimer –> nucelus –> binds to HRE –> Induces expression of target genes
-GR dimer needs co-activator
Myc/Max System
-Regulatory mechanism for gene activation or repression
Myc:
- Contains transcriptional regulation domain
- Need to be dimerized to bind to DNA
- Regulates expression of genes in cell cycle progression
Max:
- Contains DNA binding domain
- Contains dimerization domain
- Lacks transcriptional regulation domain
- Together both bind to DNA –> activate gene expression = heterodimer
- Max can form homodiemer if Myc isn’t available and repress gene transcription
Myc Overexpression
- Occurs in tumors/progression of cancer
- Disrupts equilibrium between activation and repression of genes
- Myc overexpression favors Myc/Max complexes
- Impairs differentiation and promotes cell proliferation
Expressions of the hemoglobins
-All tetramers
1) Human hemoglobin A (HbA):
- Two alpha-chains
- Two B-chains
2) Fetal hemoglobin (HbF):
- Two alpha-chains
- Two Y-Chains
3) Hemoglobin A2: (HbA2):
- Two alpha-chains
- Two S-chains
Chromosome 16:
- 2 HbA genes (Alpha-1 and Alpha-2
- Each person has 2 copies of chromosome 16 = 4 alpha genes
What are the two types of naturally forming interfering RNAs
1) MiRNA = micro RNA –> Represses mRNA translation
2) SiRNA = short interfering RNA –> mRNA degradation
Steps of miRNA
Pre-miRNA:
1) pre-miRNAs hairpin structures (by Drosha)
2) Transported to cytoplasm (by Exportin 5)
3) (Dicer) makes Pre-miRNA single stranded RNA and RNA forms RISC (RNA-induced silencing complex)
4) RISC binds imperfectly to 3’ untranslated region of target mRNA (prevents interaction of the translational machinery with the 5’ caP)
5) Inhibition of the ribosome ability to translate proteins from mRNA transcript
Steps of SiRNA
- (Dicer) makes dsRNA into siRNA
- siRNA Perfectly binds to sequence elements in the 3’ untranslated region of specific mRNA and imperfect base pairing with it
- Perfect pairing within RISC complex = activates RISC endonuclease AGO2 activity = mRNA will be cleaved and not translated = no proteins translated
miRNA and cancer
- Involved in cell proliferation
- Genes that encode these miRNA are amplified (DNA sequence = duplicated) in the tumor cells
- Cancerous cells lose cell growth regulation = cancer spreads
