Synthetic biologists at MIT have developed
"genetic circuits" that can perform basic logic functions in
living cells. In addition to performing the logic operations, the
bacterial cells in which the circuits reside can remember the
results as they are encoded into the cells' DNA and passed on for
dozens of generations.
These sorts of circuits could be used to create long term
environmental sensors or be used to programme stem cells to turn
into a particular cell type.
Most prior work in this field has focussed on either the logic
components or the memory side of things. However, the framework
developed by the MIT team combined both. Timothy Lu, assistant
professor of electrical engineering and computer science and
biological engineering, explained in an MIT news release: "We think
complex computation will involve combining both logic and memory,
and that's why we built this particular framework to do so."
Circuits in synthetic biology tend to use interchangeable
genetic components used in combination to perform a specific
function. They can be designed to perform a range of logic
functions (all 16 Boolean
logic functions) such as AND gates and OR gates. In such a
circuit, a target chemical will provoke a specific response, such
as the production of green fluorescent protein (GFP).
Lu and colleagues wanted to create a circuit that would be
irrevocably altered by the original stimulus, thus creating a
permanent memory of the event. They used memory circuits building
work from 2009 that relied on recombinases enzymes, which are
capable of cutting, slipping and inserting pieces of DNA.
The circuits had a memory function built into the logic gates,
meaning that the inputs permanently altered regions of DNA to
produce different levels of GFP. This means that the memory of the
logic gate activation is permanently stored within the DNA
sequence. To read the memory encoded in the cells, researchers can
measure the GFP output.
The team was able to create all two-input logic gates using a
library of standard parts which can be assembled into any function
using a one-step reaction.
This sort of approach could be useful in having tighter control
of the production of cells that can generate drugs or biofuels, as
it means that researchers have the flexibility to control output
levels, without having to have circuits that are always on or need
continuous inputs to control output levels. These circuits could
also provide a precise memory for environmental sensors.
The paper was published in