Regulation of Genes Encoding Virulence Factors

Question 1

Bacteria ‘sense’ several environmental factors in regulating the expression of their various virulence factors.

What environmental factors are these?

Answer 1

• Temperature
• nutrients
• oxygen (O2)
• pH inside the cell
• iron availability
• osmolarity

Question 2

What are common processes regulated at the genetic level?

Answer 2

Metabolism, response to environmental stresses and conditions, and cell division.

Question 3

What is a common system for signal transduction?

Answer 3

Many virulent bacteria have ‘global’ regulatory systems to regulate virulence factors (i.e., regulatory systems that control the production of multiple different virulence factors at once).

The virulence factors are co-ordinately regulated by a two-component system that comprises a sensor protein and a regulator protein.

Question 4

What does the sensor protein do?

Answer 4

The sensor (kinase) protein detects changes in the environment that indicate that the bacterium is residing inside a human host and then phosphorylates the regulator protein.

Question 5

What does the regulator protein do?

Answer 5

The phosphorylated regulator protein then transcriptionally activates or represses the virulence factors (e.g., flagella genes, toxin genes, adhesin genes) by binding to a DNA sequence in the regulatory regions of each of the operons for these virulence factors.

Question 6

Does the two-component system activate or block transcription of operons?

Answer 6

Depending on the particular virulence factor, the two-component system may activate or block transcription of the operons.

If the transcription of the virulence genes to be repressed, the response regulator protein would block the transcription of the DNA by the RNA polymerase (as shown in the diagram).

If transcription of the virulence genes is to be promoted, the response regulator protein would bind to the regulatory region of the operon and recruit the RNA polymerase.

Question 7

Describe the two-component regulatory system for singal transduction.

Answer 7

The sensor/transmitter is activated by a signal, resulting in a conformational change and subsequent autophosphorylation by ATP.

The phosphorylated sensor protein can then act on a regulator protein, and transfer the phosphate group.

The phosphorylated regulator protein then acts on DNA to either allow or prevent transcription of a specific set of genes.