pp 13 Flashcards
What does the sigma factor recognize?
-10 and -35 promoter elements (similar sequences to a consensus)
What does time dependent programming of gene expression result from?
switching sigma factor of the holoenzyme. Turning on transcription of multiple genes driven by promoter is recognized by a new sigma factor.
What are examples of sigma factor switching?
T4 phage infection, formation of endospores
How does the infection of B.subtilis by phage SPo1 start?
it has a long genome and has time-dependent programmed gene transcription pattern upon infection. Temporal control of transcription is divided into three parts, early, middle and late genes. During each phase, RNA polymerase holoenzyme with a different sigma factor is used that recognizes different classes of promoters
Sporulation involes switching on sporulation genes and switching off many vegetative genes, how?
By changing the sigma factors, Of, Oe, Oh, Oc, Ok act with Oa. This shows sigma factor switching is important
How does sigma-factor switching happen in E.coli?
E.coli ises the sigma factor O70 from their transcriptional activity, but it stationary phases or in starvation, alternative signma factors drive transcription of genes to respond.
What is the importance of sigma factor switches during heat shock?
E.coli turns on 17 genes called heat shock genes that code for molecular chaperones and proteases. They bind to misfolded proteins and fold them properly. The heat shock proteins are regulated by sigma factor 32.
What is nitrogen starvation?
switches on expression of o54 and o38
What is anti-sigma factors?
high temperatures and high osmolarity, E.coli makes regulator of Sigma D (rsd). This will bind to o70 and prevent it from binding housekeeping promoters.
Why is RNA polymerase switching important?
T7 phage the infects E.coli has three phases of transcription. Host RNA polymerase and o70, transcribes class I early phase genes. T7 polymerase genes are there allowing it to transcribe class II and III genes.
How does Phage Y infect?
regulates programmed gene expression using anti-termination. Since it is a temperate phage, (doesnt aways kill its host) it can undergo lysis or lysogeny.
What is the Lytic pathway?
- replication of phage DNA, breaking down host DNA
- New phage particles are produced
- Assembly of progeny phage
- Phage released from host cell by lysis
What is the lysogenic pathway?
- Phage DNA duplicated with host DNA
- Phage DNA passed on to host progeny
- Cycle repeated for many generation
What causes cell to enter lysogenic pathway?
integration of phage DNA into host DNA: low nutrient levels and high MOI
What causes lysogenic cells to re-enter lytic pathway?
Prophage induction: stress conditions
How does the lysogenic mode work?
- CI is the Y repressor, shuts down all phage gene expressions which favours lysogeny
- Cro: represses CI expression
What is lysogen?
bacterium harboring integrated phage DNA
What is a prophage?
Integrated DNA
What is the lytic mode?
-results in viral replication and rupture of host cells releasing phage particles
- it has three phases, immediate, delayed and late, if any of these are interrupted, it goes back to lysogenic pathway
Who is lytic mode time-dependent transcription pattern controlled by?
Antitermination. Genes of these phases are arranged sequentially on the page DNA
How does transcription of immediate genes in Y phage work?
- transcription begins with immediate early genes from P1 and Pr promoters
- transcription stops at terminator downstream of N gene, downstream of cro gene
- N expression allows for subsequent transcript to bypass terminators
- N: anti-terminator
How is N an anti-terminator?
Requires nut site on RNA transcript, and when it is complexed to transcript, termination signal is ignored, downstream genes can be transcribed
What is N-dependent anti-termination?
Switches gene expression program from immediate early to delayed early
What is Q-dependent anti-termination?
responsible for switching from delayed early program to late program.
- Q is delyaed early gene, that binds to DNA. If Q isnt there, RNA polymerase will stall. Q binds with qut when it is present.
