Basic Transcription Part 3 Flashcards
Lytic Phase
- infection
- phage DNA cyclizes
- decision point
- phage DNA replicates (rolling circle)
- phage heads, tails, and DNA assemble into progeny phages
- cell lysis
- reinfection
Lysogenic Phase
- infection
- phage DNA cyclizes
- decision point
- integration of phage DNA
- cell division
- phage DNA replicates
- goes through lytic cycle
Lysogenic mode
- early genes transcribed and translated by host
- lambda repressor binds 2 phage operons
- shuts down all other transcription (genes needed for lysis)
- phage integrates into host genome
lysogen
- a bacterium contining integrated phage DNA
prophage
- integrated phage DNA
when lysogen encounters mutagenic chemicals
- phage can enter lytic cycle
DNA
- linear in phage and circular soon after infection
- brings together all late genes that are separated when the phage is linear
3 phases of transcription
- immediate early
- delayed early
- late
- 3 class arranged sequentially on phage DNA
program of gene expression controlled by
- antitermination
- transcriptional switches
immediate early genes
- PL - N
- PR- cro
PL
- promoter to the left
N
- antiterminator
PR
- promoter to the right
cro
- repressor of lambda repressor
Delayed early genes for lysis
- Q antiterminator
Q antiterminator
- permits transcription of late genes
Delayed early genes for lysogeny
- CII and CIII lead to CI expression
late genes
- only transcribed when cell will undergo lysis
- not when phage integrates
immediate early genes
- host RNA polymerase binds PR and PL
- transcribes immediate early genes first
two immediate early genes
- cro
- N
- transcribed from PR and PL
polymerase encounters what when transcribing immediate early genes
- rho-dependent terminators
- encounters before delayed early genes
delayed early genes
- cro repressor blocks transcription of lambda repressor genes
lambda repressor gene
- CI
- located between two promoters
N antiterminator
- causes RNA polymerase to ignore terminators and transcribe delayed early genes
same promoters are used for
- immediately and delayed early gene expression
delayed early genes are important to
- continue lytic cycle
- establish lysogeny
Genes O and P for lysis
- Genes O and P code for proteins needed for phage DNA replication
late genes
- all transcribe in rightward direction
- not from PR
- proteins that make up phage head and tail
- proteins that lyse host cell
late promoter
- PR’
- located just downstream of Q
in absence of Q
- transcription of from PR’ terminates after 194 bases
N+Q
- anti terminators
- work via a different mechanism
Two delayed early genes help establish lysogeny
- some needed for integration of phage DNA into host genome - prerequisite for lysogen
- products of cII and cIII genes allow transcription of cI gene = lambda repressor
lambda repressor
- central component in lysogeny
- repressor of lysis
anti termination by N
- N is immediate early gene
in absence of N
- transcription from PL produces N and termination occurs downstream
N protein binds
- the N transcript at the N utilization site
- binds to its own transcript
- allows polymerase to go through rho-dependent terminator and continue on and allow readthrough
nut site
- contains an inverted repeat
- probably forms a stem loop
- RNA must loop out
processive
- anti termination factors remain associates with polymerase as it moves down DNA
- not terminated
lambda phage
- virus that infects E. coli cell
