CHE.496/2008/Schedule/Genetic circuit engineering

Genetic circuit engineering (Part 1)

• Discussion leader: Kevin

• A synthetic oscillatory network of transcriptional regulators link
  • This article by Elowitz is one of the ‘poster boys’ of synthetic biology. This is for several reasons. The first is that it was incorporated into standardized biological parts. The second is that it was very successfully modeled using a fluorescent tag at the end of each cycle. Third is the novel idea of this system. Rather than using some kind of circadian or natural rhythm, Elowitz was able to induce a completely man-made, chemical oscillating system within E. coli. Also, this oscillation occurs at a speed slower than that of natural cell division, and therefore the cell must transmit the cycle to the offspring.

• Construction of a genetic toggle switch in Escherichia coli link
  • This article discusses a bistable switch incorporated into E. coli. Like the repressilator created by Elowitz, this switch involves circuit engineering. This switch was successful in that it could be controlled between its two states. A bistable switch which randomly switches is useless. A bistable switch induced by thermal or chemical signals is very useful in biotechnology applications. For example, if a precursor was needed for a product, all the cells in the broth could produce this precursor. With a chemical or thermal signal, all the cells could then switch to producing the end product from this precursor.

KPHershey 15:35, 27 February 2008 (EST)

Genetic circuit engineering (Part 2)

• Discussion leader: Dan

• Environmentally controlled invasion of cancer cells by engineered bacteria link
  • We see the ability to detect environmental conditions linked to the expression of a useful protein - ivasin - which combined allows bacteria to invade cancerous cells. The paper is a good example of the process that is necessary for synthetic biologists to go through to properly tune a genetic circuit for the desired behavior. Their main way of tunning circuits seemed to be by creating mutant libraries of ribosome binding sites (RBS). From these they used a screen to pick the variants with the level of activity desired. It was shown that in the absence of a stimulant ivasin would not be activated. However when it was turned on invasion levels according to their assays were not very high. This may be more related to the nature of the invasin gene than the genetic circuit in use.

• Environmental signal integration by a modular AND gate link
  • Digital logic is a useful tool for programming biological organisms. This paper uses the bacteria in the previous paper and adds to the project in the form of controlling the output (invasin) using the output of an AND-gate which is fed using two of the environmental sensors. This would allow for greater specificity in the response exhibited by the engineered organisms. The authors emphasize the benefit of this work over previous works is the modularity of promises which makes it generally useful tool for engineering purposes. I would add a caveat on that in that it is useful in so far as you want to control some type of transcriptionally regulated behavior.

Daniel R Tarjan 16:58, 27 February 2008 (EST)