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Transcription attenuation for metabolic control by engineering intrinsic terminators
A main challenge in constructing synthetic biological systems is the inability to precisely regulate gene expression using artificial means. Tightly-regulated control of any given set of related transcriptional, translational and posttranslational events will likely require a combination of powerful strategies. Therefore, the 2008 Virginia iGEM team is developing a library of transcriptional terminators intentionally redesigned to be functionally inefficient. Well-characterized, standardized terminators of various efficiencies should allow finely-tuned transcription attenuation and represents yet another step toward global biological control. This work complements other gene expression control methods that focus on initiation of transcription. The desired result is quantitative control of transcript levels, which is often necessary to balance flux through a synthetic metabolic pathway. To demonstrate its potential for real-world application, the team is planning to employ this approach to control the expression of a heterologous pathway in E. coli for the biosynthesis of polyhydroxybutyrate (PHB), a biodegradable polyester plastic.
Getting in control of transcription
Terminators are never 100% efficient, meaning that not all polymerases will disengage from the strand they are operating on. This phenomenon can be exploited to create inefficient terminators we call Genetic Attentuators. Inserting a Genetic Attenuator between two genes will result in different levels of two transcripts. The levels of polycistronic mRNA will be lower than the levels of mRNA corresponding to only the upstream gene. How much lower depends on the efficiency of the attenuator.
A new technical standard!
Assembling composite BioBricks is a tedious procedure that consumes valuable time. When assembling several BioBricks, it would be nice to be able to insert a BioBrick Placeholder that could later be used to insert a BioBrick part. BioBrick Placeholders accomplish this task by providing internal restriction sites compatible with the standard BioBrick restriction sites.
Growing a renewable resource
Polyhydroybutyrate (PHB) is a polykydroxyalkanoate (PHA), a polyester polymer that is naturally synthesized by certain microorganisms. There is enormous potential for PHB production as a plastic material due to the fact that it has similar physical properties of polypropylene, a ubiquitous thermoplastic polymer derived from petroleum. Furthermore, PHB is biologically degradable.
Additions to the Registry
In addition to adding our Genetic Attenuators, BioBrick Placeholders and bioplastic parts to the Registry, we have also submitted parts that code for orange fluorescent protein (OFP), strongly enhanced blue fluorescent protein (SBFP2) and streptomycin 3'-adenyltransferase, which enables resistance to the antibiotic streptomycin