In our riboregulator system (Fig. 1), distinct promoters independently
regulate the transcription of two RNA species—a cisrepressedmRNA(
crRNA) and a noncoding, trans-activatingRNA
(taRNA). Initially, target gene translation of the crRNAis blocked
by a stem loop, which spontaneously forms in its 5′-untranslated
region (UTR), sequesters the ribosome binding site (RBS), and
prevents ribosome docking; stem loop formation is mediated by
a short sequence (cis-repressive sequence, ≈25 nt) located within
the mRNA 5′-UTR that binds the RBS. The taRNA contains
a sequence (≈26 nt) that is complementary to the cis-repressive
sequence and is capable of activating translation. When both RNA
species are expressed, the taRNA targets the crRNA and outcompetes
the cis-repressive element, leading to stem loop unwinding,
availability of the RBS for ribosome binding, and translation
of the target protein. Recently, this system was applied as the
basis for a genetic circuit that can count user-defined inputs (20).
The riboregulator system possesses a unique set of collective
features (Fig. 1), which makes it an ideal synthetic biology platform
for interfacing with and exploring different microbial systems.
These features include component modularity, physiologically
relevant protein production, leakage minimization, fast response
time, tunability, and the potential to be scaled up to independently
regulate multiple genes simultaneously. Here we apply the riboregulator
system in a series of in vivo experiments aimed at demonstrating
these advantageous features. We tracked GFP fusion
protein expression from environmentally sensitive promoters in
wild-type cells, highlighting the system’s physiologically relevant
protein production and component modularity. We also analyzed
the systems-level biological response to expression of the CcdB
toxin, illustrating the platform’s low leakage. Additionally, we
sensitively perturbed the response dynamics of a core biological
response network followingDNA damage, showcasing the tunable
gene expression and fast response time one can achieve with the
riboregulator. Finally, we computed orthogonal inputs that affect
inner membrane permeability and outer membrane integrity, respectively,
to combinatorially lyse cells, demonstrating how interoperable
riboregulators can be used to independently regulate
multiple genes inside a cell and create a programmable kill switch
for bacteria. Together, these studies show how the riboregulator
system facilitates microbiology experiments that would otherwise
prove difficult to execute using commonly used methods and
present an exciting synthetic biology tool for inducing rapid bacterial
cell death.
In our riboregulator system (Fig. 1), distinct promoters independently
regulate the transcription of two RNA species—a cisrepressedmRNA(
crRNA) and a noncoding, trans-activatingRNA
(taRNA). Initially, target gene translation of the crRNAis blocked
by a stem loop, which spontaneously forms in its 5′-untranslated
region (UTR), sequesters the ribosome binding site (RBS), and
prevents ribosome docking; stem loop formation is mediated by
a short sequence (cis-repressive sequence, ≈25 nt) located within
the mRNA 5′-UTR that binds the RBS. The taRNA contains
a sequence (≈26 nt) that is complementary to the cis-repressive
sequence and is capable of activating translation. When both RNA
species are expressed, the taRNA targets the crRNA and outcompetes
the cis-repressive element, leading to stem loop unwinding,
availability of the RBS for ribosome binding, and translation
of the target protein. Recently, this system was applied as the
basis for a genetic circuit that can count user-defined inputs (20).
The riboregulator system possesses a unique set of collective
features (Fig. 1), which makes it an ideal synthetic biology platform
for interfacing with and exploring different microbial systems.
These features include component modularity, physiologically
relevant protein production, leakage minimization, fast response
time, tunability, and the potential to be scaled up to independently
regulate multiple genes simultaneously. Here we apply the riboregulator
system in a series of in vivo experiments aimed at demonstrating
these advantageous features. We tracked GFP fusion
protein expression from environmentally sensitive promoters in
wild-type cells, highlighting the system’s physiologically relevant
protein production and component modularity. We also analyzed
the systems-level biological response to expression of the CcdB
toxin, illustrating the platform’s low leakage. Additionally, we
sensitively perturbed the response dynamics of a core biological
response network followingDNA damage, showcasing the tunable
gene expression and fast response time one can achieve with the
riboregulator. Finally, we computed orthogonal inputs that affect
inner membrane permeability and outer membrane integrity, respectively,
to combinatorially lyse cells, demonstrating how interoperable
riboregulators can be used to independently regulate
multiple genes inside a cell and create a programmable kill switch
for bacteria. Together, these studies show how the riboregulator
system facilitates microbiology experiments that would otherwise
prove difficult to execute using commonly used methods and
present an exciting synthetic biology tool for inducing rapid bacterial
cell death.
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