Virulence Regulation I Flashcards
What is an example of how bacterial genes adapt to the host environment?
Siderophores allowing them to scavenge the host for Fe
Virulence Factor
Any bacterial property required for entry, growth, or survival in a HOST - not necessarily required for life in the lab
What are examples of virulence factors?
- capsule - inhibits killing by complement
- adhesins - permit adherence to host cells
- acid tolerance factors (ASPs) - adapt pathogen to stomach
- enzymes - synthesize unavailable nutrients
Virulence Gene
Genes that encode virulence factors
Pathogenicity Islands
Large, localized regions of chromosome missing in related non-pathogens
Operator
Binding site for a transcription factor
Operon
Operon is a unit of transcription that includes more than one cistron
Multicistronic mRNA
It is the mRNA that results from transcription of a multicistronic operon
RNA polymerase
Transcribes DNA into mRNA.
σ (sigma) Factor
It is subunit of RNAP that specifically recognizes and binds the promoter
What binds to the promoter?
The RNAP holoenzyme (entire unit binds via sigma factor)
Closed Complex
The product of the RNAP/DNA interaction
Open Complex
Once bound, RNAP causes the double strand of DNA to open
What part of transcription is primarily regulated?
Initiation
What happens to cAMP as glucose decreases?
cAMP increases
What happens to cAMP as glucose increases?
cAMP decreases
What happens in the lac operon with glucose present and cAMP absent?
Repression of the operon by steric hindrance as lacR is transcribed and made into the repressor protein.
How does induction occur in the lac operon?
The inducer, in this case, lactose, will bind to the represser to prevent it from binding DNA.
Then, conditions need to be right with glucose absent and cAMP present, which will lead cAMP to bind CRP into cAMP-CRP which is the activator and recruits RNAP.
What is required for induction of the lac operon?
1) Lactose presence
2) Glucose absence -> high cAMP
What does RNAP bind?
Promoter
What does the repressor bind?
Operator - repressor binding will reduce the affinity of RNAP binding
What does the inducer bind?
Repressor - inducer binding will decrease the repressor’s binding affinity
What does the activator bind?
Activator interacts with RNAP and increases RNAP affinity
What does the co-factor bind?
In the lac operon, cAMP is the co-activator.
Co-activator binds the activator and increases the activator’s binding affinity
What happens to the probability of transcription as the stability of the closed complex increases?
The probability of transcription initiation increases as the stability of the closed complex increases.
activators increase stability
repressors decrease stability
Holoenzyme
σ + core enzyme (RNAP)
Core Enzyme
2 α subunits, 1 β subunit, β’ subunit
Regulon
A group of operons (also called a global control system) subject to the control of a common (or global) regulator
What is the purpose of a regulon?
It allows simultaneous activation and inactivation of a series of related genes
Can a repressor protein at Operator A be an activator at Operator B?
Yes
Repressors inhibit transcription by
A. increasing the affinity of RNAP for the promoter
B. interfering with the binding of RNAP to the promoter
C. causing RNAP to fall off the promoter
D. none of the above
E. all of the above
B. interfering with the binding of RNAP to the promoter
