MAJOR SHIFTS IN BACTERIAL TRANSCRIPTION Flashcards
(SIGMA FACTOR SWITCHING)
___________ of bacterium - subverts the host’s into transcription machinery
Phage infection
(SIGMA FACTOR SWITCHING)
In process, it establishes a time-independent or temporal or program of transcription:
- First early phage genes are _______
- followed by the later _____
- Reaches the late in the infectious cycle - there’s no longer transcription of the host genes, only phage genes
Changes in the genes that are transcribed - is caused by a change in transcription machinery; in RNA polymerase itself
Transcribed ; genes
(PHAGE INFECTION)
- Ɐ σ - ( For all & sigma) is the key factor in determining specificity of T4 DNA
transcription - σ - is a candidate for the shift of the transcription process
- Study of the process done in B. subtilis and its phage, SPO1
- Like T4 – SPO1 has a large genome
- ______ – has a temporal program of transcription
SPO1
(TEMPORAL CONTROL OF TRANSCRIPTION
IN SPO1)
Temporal transcription program:
o First 5 mins:
▪ Expression of _____
o After 5 – 10mins:
▪ Expression of ______
o After 10mins to end:
▪ ______ expressed
early genes ; middle genes ; Late genes
(TRANSCRIPTION SWITCHING)
___________ – is directed by a set of phages – encoded σ-factors that associate with
the host core RNA polymerase
Switching
(TRANSCRIPTION SWITCHING)
________ – change the host polymerase specificity of promoter recognition from
early to middle to late
o ________ – is specific for the phage early genes
o _________ – switches the specificity to the middle genes
o _____________ – switch the specificity to late genes
σ-factors ; Host σ-factors ; Phage gp28 protein ; Phage gp33 and gp34 proteins
(SPORULATION)
During infection, ______ – changes specificity of host RNA polymerase
Same type of mechanism applies to changes in gene expression during ________
phage SPO1 ; sporulation
(SPORULATION)
_______ – can exist indefinitely in vegetative state if nutrients are available
Bacteria
(SPORULATION)
Under starvation conditions, B. subtilis forms endospores
______________ - tough, dormant bodies that can survive for years until favourable conditions return
Endospores
(TRANSCRIPTION SWITCHING)
During sporulation:
o Whole new set of genes - is turned ____
o Many vegetative genes - are turned ____
o _____ – occurs largely at the level of transcription
o ________ - displace the vegetative σ-factors from the polymerase core and direct the transcription of sporulation genes
o _______ - has its own preferred promoter sequence
ON ; OFF ; Switch ; Several new σ-factors ; Each σ-factors
(GENES WITH MULTIPLE PROMOTERS)
____________ – must be expressed during 2 or more phases of sporulation when different σ-factors predominate
Sporulation genes
(GENES WITH MULTIPLE PROMOTERS)
Genes transcribed under different conditions – are equipped with two
different promoters
o _______ – is recognized by one of two different σ-factors
o Ensures their expression no matter which factor is present
o Allows for differential control under different conditions
Each promoter
(BACTERIAL HEAT SHOCK)
_____________ - is a defense by cells to minimize damage in response to increased temperatures
___________ – are proteins that bind to proteins partially unfolded by heating and help them to fold properly again
___________ – genes encoding proteins that help cells survive heat
Heat shock response ; Molecular chaperones ; Heat shock genes
THE OTHER σ-SWITCHES
______________ – is controlled by an alternative σ-factor, σ32 or
σH (H stands for heat shock)
Heat shock response in E. coli
(THE OTHER σ-SWITCHES)
- Directs RNA polymerase to the heat shock gene promoters
- Accumulation of σH with high temperature is due to:
▪ ____________- of σH
▪ Enhanced translation of the mRNA
encoding ___
Stabilization ; σH
(THE OTHER σ-SWITCHES)
Responses to low _____ and _________ – depends on genes
recognized by other σ-factors
nitrogen ; starvation stress
(ANTI σ-FACTORS)
These proteins – do not compete with σ-factors for binding to a core polymerase, they bind directly to σ and inhibit its function.
Example: product of the E.coli rsd gene
▪ Regulates the activitiy of the major
____________ – the product of the rpoD gene
vegetative σ, σ70 (σD)
(ANTI σ-FACTORS)
Some of the anti - σ-factors – are controlled by ___________ that bind to the complexes between a σ and an anti - σ-factors and release the anti σ-factors
anti - σ-factors
(THE RNA POLYMERASE ENCODED IN PHAGE T7)
__________– has a small genome and many fewer genes than SPO1.
Has 3 phases of transcription:
1.
2.
3.
Phage T7
- Class I
- Class II
- Class III
(THE RNA POLYMERASE ENCODED IN PHAGE T7)
_______ – is necessary for Class II and III gene expression
If gene 1 is mutated – only _______ are transcribed
o Codes for a phage – specific RNA polymerase that transcribes the ______ class II and III specifically
Gene 1 ; class 1 genes ; T7 phage
(TEMPORAL CONTROL OF TRANSCRIPTION)
________ – transcribes the Class I genes
______ of class I genes – is the phage polymerase
_________ – transcribes the class II and III genes
Host polymerase ; Gene 1 ; Phage polymerase
(INFECTION OF E. COLI BY PHAGE A)
____________ – replicate and kill their host by lysing or breaking it open
Virulent phage
(INFECTION OF E. COLI BY PHAGE A)
Temperate phage such as ___ – infects cells but don’t necessarily kill
o Have 2 paths of reproduction:
▪ ________ – infection progresses as in a virulent phage
▪ __________ – phage DNA is integrated into the host genome
λ ; Lytic mode ; Lysogenic mode
(LYSOGENIC MODE)
27 – kD phage protein (λ (lambda) repressor, CI) – appears and binds to 2 phage operator regions
____ – shuts down transcription of all genes except for cI, gene for λ repressor itself
CI
