Synthetic biology
may be viewed as an effort to establish, formalize,
and develop an engineering discipline in the context of biological
systems. The ability to tune the properties of individual components
is central to the process of system design in all fields of engineering,
and synthetic biology is no exception. A large and growing number
of approaches have been developed for tuning the responses of cellular
systems, and here we address specifically the issue of tuning the
rate of response of a system: given a system where an input affects
the rate of change of an output, how can the shape of the response
curve be altered experimentally? This affects a system’s dynamics
as well as its steady-state properties, both of which are critical
in the design of systems in synthetic biology, particularly those
with multiple components. We begin by reviewing a mathematical formulation
that captures a broad class of biological response curves and use
this to define a standard set of varieties of tuning: vertical shifting,
horizontal scaling, and the like. We then survey the experimental
literature, classifying the results into our defined categories, and
organizing them by regulatory level: transcriptional, post-transcriptional,
and post-translational.
Despite recent progress on synthetic transcription factor generation in eukaryotes, there remains a need for high-activity bacterial versions of these systems. In synthetic biology applications, it is useful for transcription factors to have two key features: they should be orthogonal (influencing only their own targets, with minimal off-target effects), and programmable (able to be directed to a wide range of user-specified transcriptional start sites). The RNA polymerase of the bacteriophage T7 has a number of appealing properties for synthetic biological designs: it can produce high transcription rates; it is a compact, single-subunit polymerase that has been functionally expressed in a variety of organisms; and its viral origin reduces the connection between its activity and that of its host's transcriptional machinery. We have created a system where a T7 RNA polymerase is recruited to transcriptional start sites by DNA binding proteins, either directly or bridged through protein–protein interactions, yielding a modular and programmable system for strong transcriptional activation of multiple orthogonal synthetic transcription factor variants in Escherichia coli. To our knowledge this is the first exogenous, programmable activator system in bacteria.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.