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Figure 3.
Vibrio fisheri
model of QS mediated, cell-density dependent regulation of gene transcription.
A) At low cell density, low levels of signal molecules (AHLs) are synthesized by LuxI and released,
and transcription of the
luxCDABEG
genes is repressed B) When cell density rises, AHLs accumulate
and exceed the threshold concentration. Signal molecules bind to the regulatory LuxR protein, that
triggers transcription of the
luxCDABEG
genes and also of the
luxI
gene (autoinduction).
When cell density increases, concentration of the autoinducer molecules rises until a certain
threshold level is reached, when signal molecules bind to the LuxR protein and activate it.
AHL-bound LuxR changes its conformation, undergoes dimerization and binds to a specific
cis
-acting inverted repeat of 18-22 pb, named the
lux box
[Sitnikov
et al.
, 1995].
Subsequently, the transcription of the
luxICDABEG
operon is triggered, resulting in the
increase of both emission of light and also 3-oxo-C
6
-HSL synthesis. However, when 3-oxo-
C
6
-HSL concentration is abundant, the LuxR-autoinducer complex starts repressing
