5,647 research outputs found
Model-guided design of ligand-regulated RNAi for programmable control of gene expression
Progress in constructing biological networks will rely on the development of more advanced components that can be predictably modified to yield optimal system performance. We have engineered an RNA-based platform, which we call an shRNA switch, that provides for integrated ligand control of RNA interference (RNAi) by modular coupling of an aptamer, competing strand, and small hairpin (sh) RNA stem into a single component that links ligand concentration and target gene expression levels. A combined experimental and mathematical modelling approach identified multiple tuning strategies and moves towards a predictable framework for the forward design of shRNA switches. The utility of our platform is highlighted by the demonstration of fine-tuning, multi-input control, and model-guided design of shRNA switches with an optimized dynamic range. Thus, shRNA switches can serve as an advanced component for the construction of complex biological systems and offer a controlled means of activating RNAi in disease therapeutics
Synthetic control of a fitness tradeoff in yeast nitrogen metabolism
Background:
Microbial communities are involved in many processes relevant to industrial and medical biotechnology, such as the formation of biofilms, lignocellulosic degradation, and hydrogen production. The manipulation of synthetic and natural microbial communities and their underlying ecological parameters, such as fitness, evolvability, and variation, is an increasingly important area of research for synthetic biology.
Results:
Here, we explored how synthetic control of an endogenous circuit can be used to regulate a tradeoff between fitness in resource abundant and resource limited environments in a population of Saccharomyces cerevisiae. We found that noise in the expression of a key enzyme in ammonia assimilation, Gdh1p, mediated a tradeoff between growth in low nitrogen environments and stress resistance in high ammonia environments. We implemented synthetic control of an endogenous Gdh1p regulatory network to construct an engineered strain in which the fitness of the population was tunable in response to an exogenously-added small molecule across a range of ammonia environments.
Conclusion:
The ability to tune fitness and biological tradeoffs will be important components of future efforts to engineer microbial communities
Creating excitonic entanglement in quantum dots through the optical Stark effect
We show that two initially non-resonant quantum dots may be brought into
resonance by the application of a single detuned laser. This allows for control
of the inter-dot interactions and the generation of highly entangled excitonic
states on the picosecond timescale. Along with arbitrary single qubit
manipulations, this system would be sufficient for the demonstration of a
prototype excitonic quantum computer.Comment: 4 pages, 3 figures; published version, figure 3 improved, corrections
to RWA derive
Exciton lifetime in InAs/GaAs quantum dot molecules
The exciton lifetimes in arrays of InAs/GaAs vertically coupled quantum
dot pairs have been measured by time-resolved photoluminescence. A considerable
reduction of by up to a factor of 2 has been observed as compared
to a quantum dots reference, reflecting the inter-dot coherence. Increase of
the molecular coupling strength leads to a systematic decrease of with
decreasing barrier width, as for wide barriers a fraction of structures shows
reduced coupling while for narrow barriers all molecules appear to be well
coupled. The coherent excitons in the molecules gain the oscillator strength of
the excitons in the two separate quantum dots halving the exciton lifetime.
This superradiance effect contributes to the previously observed increase of
the homogeneous exciton linewidth, but is weaker than the reduction of .
This shows that as compared to the quantum dots reference pure dephasing
becomes increasingly important for the molecules
Influence of the heterointerface sharpness on exciton recombination dynamics in an ensemble of (In,Al)As/AlAs quantum dots with indirect band-gap
The dynamics of exciton recombination in an ensemble of indirect band-gap
(In,Al)As/AlAs quantum dots with type-I band alignment is studied. The lifetime
of confined excitons which are indirect in momentum-space is mainly influenced
by the sharpness of the heterointerface between the (In,Al)As quantum dot and
the AlAs barrier matrix. Time-resolved photoluminescence experiments and
theoretical model calculations reveal a strong dependence of the exciton
lifetime on the thickness of the interface diffusion layer. The lifetime of
excitons with a particular optical transition energy varies because this energy
is obtained for quantum dots differing in size, shape and composition. The
different exciton lifetimes, which result in photoluminescence with
non-exponential decay obeying a power-law function, can be described by a
phenomenological distribution function, which allows one to explain the
photoluminescence decay with one fitting parameter only.Comment: 10 pages, 7 figure
Magnetic field control of photon echo in the electron-trion system: Shuffling of coherences between optically accessible and inaccessible states
We report on magnetic field induced oscillations of the photon echo signal
from negatively charged excitons in a CdTe/(Cd,Mg)Te semiconductor quantum
well. The oscillatory signal is due to Larmor precession of the electron spin
about a transverse magnetic field and depends sensitively on the polarization
configuration of the exciting and refocusing pulses. The echo amplitude can be
fully tuned from maximum down to zero depending on the time delay between the
two pulses and the magnetic field strength. The results are explained in terms
of the optical Bloch equations accounting for the spin level structure of
electron and trion.Comment: 8 pages, 2 figure
Optical control of coherent interactions between quantum dot electron spins
Coherent interactions between spins in quantum dots are a key requirement for
quantum gates. We have performed pump-probe experiments in which pulsed lasers
emitting at different photon energies manipulate two distinct subsets of
electron spins within an inhomogeneous InGaAs quantum dot ensemble. The spin
dynamics are monitored through their precession about an external magnetic
field. These measurements demonstrate spin precession phase shifts and
modulations of the magnitude of one subset of oriented spins after optical
orientation of the second subset. The observations are consistent with results
from a model using a Heisenberg-like interaction with microeV-strength.Comment: 5 pages, 4 figure
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