Information Technology Reference
In-Depth Information
Figure 4.18
Transfer band thresholds: high and low input ranges for a hypothetical
inverter. The transfer band, capturing systematic fluctuations in signals, is defined by
the two curves.
min
(
J
il
),
J
max
(
0
)
⊂
J
I
ih
,
∞
max
(
J
ih
)
⊂
0
,
J
0
,
I
il
.
Then, assuming monotonic functions, the following conditions are necessary
and sufficient for correct coupling:
min
(
J
il
)>
I
ih
J
max
(
J
ih
)<
I
il
.
J
Genetic Process Engineering
The first step in developing biocircuits is designing, building, and characterizing
several inverters. It is likely that these inverters will not match correctly ac-
cording to the definitions above. Fortunately, there are biochemical techniques
to adjust inverters to obtain the correct behavior for use in complex circuits
(Figure 4.19). These are described below.
MODIFYING THE REPRESSOR/OPERATOR BINDING AFFINITY Certain basepair
mutations at an operator site alter the affinity of the repressor to the opera-
tor. As illustrated in Figure 4.19a, weakening the repressor affinity shifts
C
,
the cooperative binding stage mapping the input signal,
φ
A
, to the repression
activity,
ρ
A
, outward to the right. For a given level of the input repressor protein,
there is now less repression activity than before the mutation. The mutations
