Gene Regulation: Lect 13 Flashcards
Constitutive gene
“housekeeping” gene; always expressed within a cell.
Regulated gene
only expressed under certain conditions.
- Repressor: prevent RNA poly from initiating transcription.
- Activator: allows RNA poly to transcribe.
Operator
binding site for proteins that help to regulate gene expression; it is adjacent to the promoter.
Lac operon:
-LacZ:
-LacY:
-LacA:
share same promoter and operator. LacP and LacO
used to study the regulation of genes required for the metabolism of lactose in bacteria.
- only expressed in the presence of lactose*
- B-galactosidase (lactose > gluc +gal) (lactose > allolactose)
- Permase: active transport of lactose across the CM.
- Transacetylase: gal >acetylgal
lacl - encodes a repressor protein in absence of lactose.
Lactose added?
Allolactose binds to repressor and dissociates from operator. RNA poly initiates transcription
Negative control:
Positive control
- when repressor is used to turn system off.
- when activator is used to increase rate of transcription.
Bact prefers glucose as a carbon source.
No glucose? and lactose present…
- hunger signal
- cAMP is produced and binds to CRP/CAP which binds to the lacP to help activate transcription.
Lac/gluc present:
Lac present/gluc absent:
Lac absent/gluc present:
Lac/gluc absent:
System OFF
System ON
System OFF
System OFF
Cis regulatory elements:
- DNA binding sites; TF/enhancer binding site.
- Basal promoter seq: CAAT, TATA, GC box. Interact w/ RNA poly, allow low level of expression.
-Proximal control regions: bind TF near the promoter. Increase expression and provide specificity
- Enhancer seq: found far away from the promoter. More specificity and amplify expression.
- bending allows interaction w/ TFs; high level of transcription
Trans regulatory elements:
-TFs and enhancer binding proteins.
TFs as repressors:
Competition:
Quenching:
Blocking:
- repressor binds to enhancer seq on the DNA.
- repressor binds to and interferes w/ DNA bind domain.
- repressor binds to activation domain
Hypoxia Response Elements:
- HIF1a and HIF1B factors must dimerized to regulate expression.
- regulates genes on diff chrom
- under normaxia, Hif1a is degraded in the cytoplasm.
- under hypoxia, Hif1a is not degraded and enters the nucleus where it heterodimerises w/ Hif1B.
Glucocorticoid receptor
- zinc finger type TF
- upregulates expression of anti-inflammatory genes in nucleus. Represses pro-inflam genes in cytosol.
- absence of glucocorticoid; GR held in cytoplasm.
Myc/Max system:
Myc: has transactivation domain and no homodimer.
Max: form homodimers, binds to DNA but no transactivation domain.
Myc regulates expression of genes in cell cycle. It won’t bind to DNA unless it dimerizes.
-Absence of Myc, Max forms a homodimer and represses transcription.
- Presence of Myc, Myc/Max heterodimer => cell proliferation.
- –overexpression of Myc = cancer
VDJ recombination
-can result in lymphoid cancers that bring Myc under control of Ig promoter and enhancer seq.
