L13: Transcriptional Regulation in Prokaryotes II (bacteriophage λ) Flashcards
(38 cards)
explain bacteriophage lambda (λ)
it infects E. coli and undergoes either:
1. lytic growth
2. lysogenic growth
what is lytic growth
- reproduction of viruses
- uses the host cell to product more viruses and then it bursts out of the cell
what is lysogenic growth
- virus reproduction
- phage genome integrates itself into the E. coli genome through site-specific recombination
- this cell then becomes a prophage
what is a prophage?
a dormant phage in lysogenic phase
explain the regulatory region of bacteriophage lambda (λ)
- three promoters:
1. P-RM
2. P-L
3. P-R
regulatory region of bacteriophage lambda (λ) - P-RM
- repressor maintenance
- active during lysogenic growth
- its a weak promoter that requires an activator to induce gene expression
- it transcribes the cl (l = 1) gene than encodes lambda (λ) repressor
P-RM - what are the two domains of the lambda (λ) repressor
- amino-terminal DNA binding domain (helix-turn-helix motif)
- carboxyl-terminal dimerization domain
P-RM - what can lambda (λ) repressor act as
- a repressor
- an activator
lambda (λ) repressor - acting as a repressor
by binding DNA and physically excluding RNA Pol
lambda (λ) repressor - acting as an activator
by binding DNA and recruiting RNA Pol using an activating region on the amino terminus
regulatory region of bacteriophage lambda (λ) - P-L and P-R
- both are active during lytic growth
- Cro is a dedicated repressor transcribed from P-R and it binds as a dimer using a helix-turn-helix motif
what are the operators
- multiple operators can be bound by the lambda repressor and Cro
- operator O-R1
- operator O-R2
- operator O-R3
explain operator O-R1
- in promoter P-R
- has the greatest affinity for lambda repressor
explain operator O-R2
- overlaps with P-RM and P-R
- the cooperative binding at O-R1 helps recruits the lambda repressor to O-R2
explain operator O-R3
- in promoter P-RM
- has the greatest affinity for Cro
what is the gene layout in lysogenic stage
- P-L promoter
- cl gene
- P-RM promoter (all of O-R3 and some of O-R2) ←
- P-R promoter (some of O-R2 and all of O-R1)
- cro gene
what is the gene layout in lytic stage
- P-L promoter ←
- cl gene
- P-RM promoter (all of O-R3 and some of O-R2)
- P-R promoter (some of O-R2 and all of O-R1) →
- cro gene
what happens to the gene layout during lytic growth
- the Crop repressor dimer binds O-R3 at P-RM
- RNA Pol then binds to P-R and P-L to activate lytic genes
lytic growth - what does binding O-R3 at P-RM do?
it prevents the RNA pol from transcribing the lambda repressor
lytic growth - what happens after the binding of RNA Pol
- lytic genes are activated
- no basal activation bc P-R and P-L do not require activators since they are strong promoters
what happens to the gene layout during lysogenic growth
- the lambda repressor dimer binds O-R1 at P-R
- cooperative binding of lambda repressor spreads to weaker O-R2
- activating region of lambda repressor at O-R2 brings RNA Pol to P-M
lysogenic growth - what does binding O-R1 at P-R do?
prevents RNA Pol from binding and activating cro expression
lysogenic growth - what does the recruitment of RNA Pol to P-RM do?
results in expression of more lambda repressors (positive autoregulation)
how does the cell choose between lysogenic and lytic development?
- its dictated by growth conditions of E. coli
- growth conditions affect the stability of the regulator cll (II = 2)
- the activity of Cll dictates lysogenic vs lytic development
- cII activity is dictated by HflB
