Lecture 12: Regulatory Systems

Question 1

Global regulatory systems

Answer 1

• catabolite repression
• sigma factors
   Virulence gene expression
   Quorum sensing
   Sporulation

Question 2

catabolite repression

Answer 2

diauxic growth

Question 3

sigma factors

Answer 3

 7070 normal conditions
 Stress responses
 3232 heat shock
 Differ in -35, -10 seq

Question 4

signal transduction

Answer 4

 Change gene
expression
 Alter physiology
 Much more closely
tied in bacteria
than in Euks
 Phosporylation!
 Phosphorelay
system

Question 5

Sporulation in Bacillus

Answer 5

• Activation of sporulation transcription factor
  Spo0A
   2-component phosphorelay
   Activates genes in endospore formation
• signal ATP:ADP ratio

Question 6

Quorum Sensing

Answer 6

 All known bacteria use AI-2,All known bacteria use AI-2,
halogenated furanone signal
 Function, mechanism unclear
 Gram positive
 peptide pheromones
 cell surface
 Gram negative
 Acyl-homoserine lactones

Question 7

Quorum sensing in virulence

Answer 7

 Pseudomonas aeruginosa
 LasR/Las - 3OC12HSL
 RhlR/RhlI-C4HSL
 Two different AHLs!
 Control virulence
factor production
 Integrated into a larger system to control
- cyclic-di-GMP

Question 8

Cyclic Nucleotides

Answer 8

 Used as “cell state” regulators
 cAMP – metabolic health
 c-di-GMP used toc-di-GMP used to integrate competing
signals
 Used in many different bacteria

Question 9

Repression

Answer 9

 Repression inhibits gene expression
 A protein acts as the repressor by binding to the DNA and preventing transcription
 The repressor may bind only in the presence of a co-factor, which may itself be a product of the structural gene

Question 10

Induction

Answer 10

 Induction is the process by which a set of genes is turned on by the presence of an inducer
 In many cases, the inducer is a substrate for the gene system or operon
 An operon is defined as a set of genes that are contiguous in the genome and coordinately regulated
to encode some functional genes
 A repressor and inducer may work together to regulate the expression of the genes in an operon

Question 11

The Lac Operon

Answer 11

 Parts of the operon- structural genes lacZYA, regulatory gene lacl, promoter regions and operator region (site where repressor binds)
 When lactose is absent, repressor binds, prevents transcription
 When lactose is present, it binds to LacI, prevents it from binding DNA, allows transcription to be induced

Question 12

Catabolite Repression

Answer 12

 Lactose can act to induce lac operon, but what if lactose and glucose are present?
 Glucose is the preferred substrate, and this is effected using catabolite repression
 The effector protein is CAPThe effector protein is CAP (crp gene), which binds cAMP, inversely proportional to glucose