Lambda Repressor Flashcards
The DNA binding form of repressor is a
dimer so 2 DNA-binding domains can contact operator simultaneously
a repressor monomer has 2 distinct regions:
- N-terminal domain: contains DNA binding site
2. C-terminal domain dimerises
We can induce lytic cycle by
Cleavage of repressor between domains -> reduces affinity for operator
What motif does the repressor use to bind DNA?
helix-turn-helix
Each DNA-binding region in repressor contacts a ____ in DNA
half-site, palindromic sequence of 17 bp
Why does DNA binding protein of repressor have short alpha helical regions?
The fit into the major grooves of DNA -> increase affinity
How does lambda repressor dimer bind cooperatively to operator?
The operator region has 3 binding sites each with 2 half sites. Affinity for OL1 and OR1 is 10x greater so binds first here. OL2 and OR2 require lower conc.’s. OL3 and OR3 only at high conc’s.
OR2 binding function
adjacent to PRM so host RNAp. recognises PRM when repressor is bound to OR2
OR3/OL3 binding function
turns off transcription of lambda repressor
Cro has a _____ structure to c1 and binds _____ first
homogenous, OR3/ OL3
Cro _____ have co-operative binding
doesn’t
OR3
prevents RNAp from binding to PRM + turns off expression of lambda repressor
Cro can turn off ____ but only at _____ because ____
PL/PR, end of lytic cycle, early genes not needed
How does lambda repressor maintain an auto-regulatory circuit?
- DNA binding region of repressor at OR2 contacts RNAp and stabilises its binding to PRM
- Binding at OL block transcription of gene N from PL
- Binding at OR blocks transcription of cro but also necessary for ci
How do co-operative interactions increase sensitivity of regulation?
Repressor dimers bound at OL1 and OL2 interact with OR1 and OR2 to form octamers to increase sensitivity
