Lecture 8
? 8.8 Attenuation
? 8.9 Other Global Control Networks
? 8.10 Signal Transduction and Two-
Component Regulatory Systems
? 8.11 Regulation of Chemotaxis
RNA and termination
? RNA,single stranded nucleic acid
– can form secondary structures
? Rho-dependent termination,protein signal
? Rho-independent signal,hairpin or stem-
loop RNA structure,followed by several
uracils
Figure 8.20
Tryptophan Operon
Tryptophan Operon,mRNA
1 2 3 4 trpE ?
? regions 1,2,synthesis of leader peptide
? regions 2,3,form stem-loop structure
? regions 3,4,form stem-loop structure
Figure 8.21
Attenuation
Figure 8.22 Bioluminescent Vibrio fischeri
Vibrio bioluminescence
? Vibrio fischeri inhabits
the open sea (in small
densities),as well as in
squid light organs (in
high densities)
? Luminescence occurs
only at high cell
concentrations
Quorum Sensing
? Regulation of genes expression in response to
population density
? Acylated homoserine lactone (AHL) molecules might
be produced and excreted by all cells in a given
population
? Higher population density results in greater
concentration of AHL
? AHL molecules activate a specific transcriptional
activator protein,resulting in specific transcription
induction
Quorum-sensing model from University of Nottingham
Quorum Sensing Research Group (Paul Williams)
Two-component regulatory
system
Figure 8.23
Chemotaxis
Figure 8.24
Chemotaxis in Review
? no attractant,CheA?CheA-P,CheY-P
– tumble
? attractant,MCP blocks CheA-P
– CheZ,CheY-P?CheY
– run
? over time,CheR methylates,desensitizes MCP
– new baseline,as if no attractant present
– CheA?CheA-P,CheY
– tumble
– CheB-P demethylates,re-sensitizes MCP
Taxis Receptors
? multiple MCPs sense different substrates
? other,similar systems respond to different
conditions (light,oxygen,etc.)
? taxic responses studied by mutational
analyses