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iGEM 2007

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Viral Smart Bombs

iGEM is an international synthetic biology competition between teams at various universities. Each team designs and implements a genetic system which performs a task. This system should use parts taken from the Registry of Standardized Biological Parts ("Biobricks") whenever possible, to prove that devices and system in bioengineering, much like those in other engineering fields, can be made from standardized parts. Parts standardization improves the predictability of engineered systems and reduces or eliminates the need for the bioengineer to construct his/her own parts, leaving him/her free to focus on overall system design. If a part used during the competition is newly designed due to a lack of an equivalent RSBP part, then the part will be entered into the registry.

Enterobacteriophage λ is a temperate virus that infects Escherichia Coli cells. Once inside the cell, λ chooses between two pathways. It can enter the lytic pathway, in which it uses host cell machinery to manufacture copies of itself and eventually releases them by lysing the cell. It can also enter the lysogenic pathway, in which it inserts its genome into that of the host where it is replicated along with the host genome. We want to manipulate λ's decision in response to molecular signals inside the host cell, so that it only lyses a specific subpopulation of cells. If successful, this will give us more insight on how life cycle decisions are made in the λ bacteriophage.

A schematic of lambda's life cycle.

There are three control points in the λ genome we want to regulate: cro, N, and Q. Using three control points gives us more control over λ's life cycle, as well as providing us with redundancy in case one of the regulatory systems don't work.

Riboregulators a form of post-transcriptional gene expression control. A riboregulator consists of a cis-repressor, which acts as a lock, preventing translation, and a trans-activator, the "key" that allows translation. The cis-repressor consists of a region complementary to an mRNA transcript's ribosome binding site (RBS) and a short loop, both upstream of the RBS. When transcribed, the complementary region binds to the RBS, preventing ribosomal access. The trans-activator, also an mRNA, contains a stem-loop structure as well as a region complementary to the cis-repressor. When introduced, the trans-activator binds to the cis-repressor, allowing ribosomal access to the RBS of the riboregulated gene.


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