bacteria need to adopt with their surrounding environment .regulons are one of the tools that bacteria use for this adaptation.

1. Investigating Regulon Global
Mechanism In Bacteria
Gathered by : Afagh Bapirzadeh
Molecular Genetics Doctorate Student
Supervised by: Dr. Tabatabaei

2. Investigating Regulon
Mechanism In Bacteria By
Fur And Pho Regulon Function

3. What Is A Regulon
It is a group of genes regulated as a unit ,generally controlled by the
same regulatory gene.

4. Why using Pho regulon
• To adapt and survive in different microenvironments, bacteria
must sense and respond to extracellular signals.
• The adaptive response to stimuli follow a two –component
regulatory systems
1-an inner-membrane histidine kinase (HK) sensor protein
2-response regulator (RR) that acts as a DNA-binding protein,
activating or repressing gene expression
The extracellular phosphate is regulated by PhoBR in which PhoR
encodes the HK and PhoB encodes the RR.

5. Importance Of Phosphorus For Cell Survival
1.Phosphorus is the fifth most important
element in terms of cellular content
2.It is important for biological processes:
inheritance of genetic materials, energy metabolism,
membrane integrity and intracellular signaling
 The main assimilable form of phosphorous in
bacteria is the orthophosphate anion=inorganic
phosphate(Pi)

6. Pho Regulon Component
• Common members activated by Pho regulon are:
1.Extracellular enzymes capable of obtaining Pi from organic phosphate
Alkaline phosphatase , phospholipase, glycerophosphodiester
phosphodiesterase,phytase,5-nucleotidases are the most common enzymes induced in
response to Pi starvation in bacteria
2.Pi-specific transporters
The Pst Pi-specific transporter is the most conserved member of Pho regulon in all
bacteria
3.Enzymes involved in storage and saving of the nutrient
For the storage of Pi ,most bacteria induce the expression of PpK
PpK is able to accumulate polyphosphate as a Pi reservoir and when needed, reuse it.
Some bacteria are able to replace teichoic acids by teichuronic acids

7. PHO Box
• In 1988,Makino et al introduced PHO Boxes
• They are specific DNA sequences that
activate or repress the transcription of
specific genes in Pho regulon
• The PHO Box sequences vary from one
species to another
• PHO Box sequences depends on the specific
contacts that the amino acids of response
regulator are able to eject with the bases of
the DNA

8. Mechanism
Of Action In
Pho Regulon
Phosphate
starvation
PhoBR is
activated(phosphorylated
by HK)
Genes under Pho regulon
start being transcribed or
repressed
Phosphorylated PhoB binds
to specific DNA
sequences(Pho-box)
The Pst system encodes
an ATP binding
Cassette(ABC)
transporter
The Pst is involved in
transporting inorganic
phosphate

9. Phosphate rich
environment
PhoU & PhoR
dephosphorylate PhoB
PhoU controls Pst
system
Dephosphorylated
PhoB binds to DNA
and play its role in
transcription
Pst system is not
allowed to enter
phosphate

10. Pho Regulon And Bacterial Virulence
I. Extra-intestinal pathogenic E.coli are an important group of
pathogenic E.coli
II. The role of Pho regulon in virulence of these bacteria is proven
when the attenuation of virulence of mutant strains correlated
directly with the level of activation of the Pho regulon.
III. Selective capture of unique transcribed sequences(scots)
revealed that fine-tuning of the Pho regulon is required for
virulence ,while inappropriate or constitutive induction of the
Pho regulon has deleterious effects.

11. The Pho Regulon Is Involved In Pathogenesis
Several Strategies
For Virulence By
Pho Regulon
Tolerance to acidity
Toxin production
Biofilm formation
Resistance to antimicrobial compounds

12. Fur regulon
investigation
in bacteria

13. Iron Importance In Bacterial Cell Survival
• Iron is essential for cell growth and survival for most bacteria
• In neutral PH and aerobic conditions. Iron limitation is a big challenge
• iron can also be toxic to cells more that needed and produces oxygen radicals
• So bacterial cells need a regulatory system to maintain iron homeostasis

14. Fur Regulon definition & Function
Fur
regulon
Regulating
Iron
acquisition
genes
Involved in
energy
metabolism
Involved in
redox-stress
resistance
Involved in
chemotaxis
Involved in
metabolic
pathways
Involved in
toxin
production
Involved in
swarming
Involved in
DNA
metabolism
Involved in
TCA cycle
• Ferric Uptake Regulator =Fur
• Senses intracellular iron availability
and plays crucial role in maintaining
iron homeostasis
• In iron deficiency conditions ,Fur
regulon derepressed in three waves.

15. Fur Molecule Parts There are three metal-binding sites(1,2,3)
Site 1 : is the structural zinc site required for
protein folding
Site 2 & 3 : are occupied by metal in the
functional holo-repressor
Metal first binds at site3 with subsequent
binding to the key allosteric site (site
2)leading to more than 100 –fold increase in
DNA binding affinity

16. Fur -Box
It is in promoter region
It consists of 19-nucleotide
Before -10 and after -35
Fur protein bind this region

17. Fur regulon second mechanism in E.coli
• Typically targets
mRANs encoding
iron-using or iron-
binding proteins
This will result in
preserving iron
levels in the cell
RyhB sRNA
Is Responsible For
Destabilizing mRNA
Of Target Genes
• Fur blocks the
transcription of
downstream genes
It negatively
regulate genes by a
gene coding the
small regulatory
RNA named RyhB
Fur Acts As
Repressive
Regulator
• At least 2 zinc
ligands per
monomer stabilize
the dimer
• Iron binding causes
conformational
changes enabling
Fur to bind to its
DNA target
Homodimer Fur
Binds To Fur-boxes
LOW IRON
CONDITION
WILL BE
MANAGED

18. Stepwise Regulation Of Genes Derepressed Under Fur Regulon
H.pylori
Fur mediates direct activation via variable mechanisms.
An iron-bound Fur dimer binds to a site further upstream
of -10 and -35 motifs in the promoter region and out-
competes binding of a repressor protein, thus activating
transcription . Without iron, Fur does not function and the
repressor protein binds to the promoter region to repress
gene transcription