Information Technology Reference
In-Depth Information
OO
OO
OO
O
O
O
H
H
H
OO
O
OO
O
O
O
O
O
OO
H
H
O
OO
O
O
Low Cell Density
OO
O
O
High Cell Density
H
OO
Low Cell Density
High Cell Density
O
OO
OO
O
H
O
O
O
H
H
O
H
O
H
O
OO
OO
OO
OO
O
O
LuxR
LuxR
O
O
OO
H
H
O
O
H
H
O
O
O
O
H
(Light)
hv
(Light)
hv
Luciferase
Luciferase
LuxR
LuxI
LuxR
LuxI
(+)
P
P
luxR
luxI
luxC luxD luxA luxB luxE luxG
luxR
luxI
luxC luxD luxA luxB luxE luxG
P
P
symbiotic, 10 10 cells/liter
800 photons/second/cell
free living, 10 cells/liter
< 0.8 photons/second/cell
Figure 7.14 The lux operon and quorum sensing: density-dependent biolumin-
escence.
the C-terminal helix-turn-helix DNA-binding domain. The LuxR protein acts
as a transcriptional activator for the RNA polymerase holoenzyme complex.
The activated protein likely binds in dimeric or multimeric forms because of the
evident dyadic symmetry of the Lux box binding domain. Figure 7.14 shows
the genetics of bioluminescence in two distinct environments in which Vibrio
fischeri naturally occurs. The dimeric binding of the LuxR product to the op-
erator produces the kind of nonlinear concentration/response behavior [8, 16]
and widely seen in DNA-binding protein transcriptional control. This nonlin-
ear response is an essential element of signal restoration and digital control of
expression.
Successful cloning and expression of the Lux genes into E. coli have estab-
lished the genetic structure of the Vibrio fischeri Lux operon [3]. It is somewhat
surprising (although common) for the transfer of regulatory genes and entire
metabolic pathways to function straightforwardly across Gram-negative species
boundaries in this way.
Intercellular Signaling Experiments
To experiment with engineered cell-to-cell communications, we constructed a
series of plasmids, as described elsewhere [15]. The plasmids encode genetic
logic circuits that enable cells to send messages and logic circuits that enable
cells to detect and respond to incoming messages. This section describes exper-
iments to characterize the cell-to-cell communication capabilities engineered
into E. coli cells using these genetic circuits.
Sending a Constant Cell-to-Cell Signal
The first intercellular communications experiment involved sending a constant
signal from one cell type to another. The pSND-1 plasmid encodes a circuit that
 
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