Gene Regulation Flashcards
Attenuation
- way to couple Tc to nutrient supply-dont make genes for aa biosynthesis if you already have the aa
- common mode of regulation for aa synthesis
- leader sequence codes for peptide that functions as the attenuator
- lots of trp-make leader, Tc halted
- low trp- do not make leader, Tc goes ahead
Trp Operon
- high Trp levels-the message is read quickly, favours formation of terminator (1/2, 3/4)
- low trp-ribosome stalls, favours formation of anti terminator (2/3)
Jacques Manod
-worked out gene regulation for lac and trip operon
Repressors and negative control
- proteins that bind DNA
- bind to specific sequences called operators
- repressors block binding of RNA pol to promoter
- ability to bind DNA is often regulated by cofactors (sugars/metabolites)
LacZ
-beta galactosidase-cuts disaccharide lactose into glucose and galactose
LacY
-permease-lets lactose into the cell
LacA
-beta galactosidase transacetylase
LacI
repressor
P
promoter
IPTG
artificial inducer
Tools available to Jacob and Manod
- mutants (constitutive, non-inducible)
- construction of merodiploids (having a second copy of an allele), allowed for complementation
- assay for enzyme activity to tell if gene was being expressed or not
Lac operon-Uniduced State
- LacI binds operator
- no Tc
Lac operon-non-inducible mutants
- lacZ
- lacIs repressor can no longer bind lactose
Lac operon-induced state
- inducer (lactose or IPTG) binds LacI
- LacI cannot bind operator
- Tc of operon
Constitutive Mutants
- lacI-no repressor, no repression
- Oc-repressor binding site damaged, LacI is made but can’t bind
Cis and trans mutations
- cis acting locus-a genetic region affecting the activity of genes on that same DNA molecule (ex. lac operator)
- transacting locus-encodes for a factor that can act elsewhere (LacI)
Activators-positive control
- proteins that bind specific sequences of DNA
- make contact w/ RNA pol
- recruit holoenzyme to promoters
- classified by structure of DNA binding domain
Diauxic shift and catabolite repression
- cells use glucose first
- presence of glucose represses many genes
- glucose downregulates the activity of adenylate cyclase which makes cAMP
- cAMP binds catabolite activator protein CAP
- CAP (w/ cAMP bound) is an activator that recruits RNA pol to promoters that would not be turned on efficiently otherwise
Positive Control in lac operon
- subject to catabolite repression
- CAP binding site adjacent to promoter recruits pol for efficient Tc
Negative Control-Trp Repressor
- operator region is bound by repressor
- repressor is only able to bind DNA when bound to Trp
Flagella Synthesis
- 50 genes to make a flagella
- flagellin is among the most abundant proteins synthesized in the cell
- tightly controlled
- Tc cascade
- alternate sigma factor, sigma 28, regulates Tc of late genes
Sigma factor-antisigma factor
- FliA encodes alternate sigma factor
- FliA directs polymerase to late flagellar genes
- FliA is in complex w/ FlgM (anti sigma factor)
- when hook-basal body are complete, Flgm is secreted
Sigma 54
- sigma 54 RNA pol cannot form open complex on their own
- need help of NtrC at enhancer sequences far upstream from promoter
- they bind RNA pol and allow the genes to be Tc b/c of structural change in the DNA (make open complex)
