BC 20 Control of Gene Expression Flashcards
how can we control gene expression
- Transcriptional
- RNA processing
- RNA transport control
- translational control
- mRNA degradation control
- protein activity control
refer to first few slides for any you cant define
Transcription Regulation
Cis Elements: DNA sequences where the transcription factors bind.
Trans acting elements gene regulatory proteins that recognize cis elements
Upsteam promoter elements: the promoter region os where the RNA pol binds to and beings its RNA synth. tata in human or -10 -35 in bac
Operon
functional unit under the control of a single promoter
includes regulatory (promoter/operator) and structural genes
Bac: polycistronic-group of proteins in same frame required for same metabolic fxn, one message, multiple ORFs- SAME biochemical pathway
lac operon
Bacterial operon
glucose used for energy, lactose provides enery source broken down by B-galactosidase to glucose and galactose
-lac operon drives group of proteins involved in this pathway.
inducible system: always off unless lactose (inducer) present
lac operon positive control
low/no exogenous glucose
- adenylatecyclase is activated at low glucose
- cAMP concentration increases
- cAMP binds to catabolite activator protein (CAP)
- complex binds at CAP site
- CAP interacts with RNA pol, makes promoter more accessible
- bends DNA to enhance RNA pol binding
-high levels of exogenous glucose will repress gene expression by lowering the cAMP levels, preventing cap fro binding
lac operon negative control
- transcription of the operon is controlled by o (a regulatory sequence)
- lac repressor is encoded by I gene
- I gene is constitutively expressed
in ABSENCE of lactose
- lac repressor binds to operator preventing transcription from lac operon
- no transcription, neg control
in PRESENCE of lactose (inducer)
-lactose binds repressor and removes repressor from binding to the operator.
for lac operon to express must not only block repressor but also positive effect (CAP)
Euk Gene transcriptional regulation
3 RNA pols.
- RNApol I for RNA’s
- RNApol II for protein coding genes
- RNApol III for tRNA, rRNA, snRNA
-all multiunit complexes and regulated by a variety of GTF
tataa
upstream promoter element for RNApolII to bind
Enhancers
Cis acting elements to enhance expression
- activators bind to enhancers and regulate GE
- can only act on CIS linked promoters. (on same chromosome)
- upstream or downstream
- can be KB away
- ORIOENTATION INDEPENDENT
- distance and position independent
DNA looping
enhancer function
activators bind to enhancer sequences and DNA loops for activator to complex with various TF’s
Tissue specific
DNA biding protiens only work in specific tissues. IG heavy chain enhancer, NINE different reg proteins.
-sum effect between these, not all bound at once necessarity
Activators
trans acting elements
two domains, binding (sequence specific) and activating domain
Four binding domains
Zinc Finger Binding domain
zinc ions fold loops that bind DNA
zinc binds cysteine, cysteine, histidine, histidine
steroid hormone receptors function int this way.
- regulate GE in response to hormones such as est and test
- cis element =hormons response element
Leucine Zipper and Helix Loop Helix
both have dna binding domain formed by dimerization of the PP chains
leucine:
-CREB -cyclic AMP response element binding protein
HLH: myc TF- Ebox
Different members of each family can dimerize with another- heterodimerizatio, increases possible number of recognition sequences
Helix Tun Helix
one helix makes most of contact with DNA other helix lays across it to stabilize it.
HOX proteins
- embryonic dev
- cis element :homeobox
- fused fingers
- arms out of eyes drosophila
