User:Cheuk Ka Tong/Sandbox3

=Cell-Free Systems=

Introduction
An important aspect of our project is to investigate the use of cell-free systems (CFS) to realise new potentials for simple constructs. To date, work on synthetic biology has been done using the chassis of bacterial cells. However the use of living, replicating engineered bacteria poses a huge limitation for applications in the food and medicine industries for reasons of public safety. In line with the specifications of our two genetically engeineered machines - Cell by Date and Infector Detector, our team decided to introduce cell-free expression systems as a new chassis to the field of synthetic biology.

Types of Cell Extracts
In-vitro synthesis of proteins using cell-free extracts consists of two main processes - transcription of DNA into messenger RNA (mRNA) and translation of mRNA into polypeptides. Coupled transcription-translation systems usually combine a bacteriophage RNA polymerase and promoter (T7, T3, or SP6) with eukaryotic or prokaryotic extracts. In addition, the PURE system is a reconstituted CFS for synthesizing proteins using recombinant elements.

Comparison between different types of cell extracts

Types of Compartmentalization
Previous research has been done to optimize cell extracts for in vitro protein synthesis. Their endogenous genetic content is removed so that exogenous DNAs or mRNAs can be expressed. Nuclease activity has been reduced and degradation of certain amino acids has been identified. ATP regenerating systems have also been added to improve the energy supply. Different strategies of compartmentalization have been explored to prolong the lifespan of CFS.


 * 1) Batch-mode CFS
 * 2) *Transcription-translation reaction is carried out in bulk solution. Expression is usually limited by nutrient (nucleotides and amino acids) and energy supplies.
 * 3) Continuous-exchange CFS
 * 4) *Transcription-translation reaction is separated from feeding solution by a dialysis membrane. Expression is sustained by diffusion of nutrients from the feeding soltuion to the reaction. Wastes generated by the reaction is diluted in the feeding solution.
 * 5) Liposome-encapsulated CFS
 * 6) *The reaction is separated from feeding solution by a phospholipid bilayer. Expression is maintained for a longer time period than batch-mode CFS because of exchange of materials between the reaction and the feeding solution across the membrane. More reliable exchange of materials is established by inserting a non-specific pore protein with a suitable channel size into the phospholipid bilayer.

Achievements
To get around the problem of having bacteria in contact with food or medical devices in the applications of Cell by Date and Infector Detector respectively, we aimed to express reporter DNA constructs within a CFS consisting of cell extract encapsulated in selectively permeable vesicles. Our plan was to first prepare the cell extract and perform in-vitro expression in bulk solution. In parallel, we would investigate and optimize conditions for phospholipid vesicle formation. The final stage of our project would involve combining the two, so that protein expression is achieved inside the vesicles.

In-Vitro Expression

 * Attempted to make S30 E. coli cell extract and feeding solution
 * Successfully used commercial S30 E. coli cell extract and feeding solution from Promega for expression of GFP
 * Successfully used homemade S30 E. coli cell extract with commercial feeding solution for expression of GFP
 * Attempting to characterize the temperature range and timespan of expression of our reporter DNA constructs using commercial S30 E. coli cell extract and feeding solution

Vesicle Formation

 * Successfully formed empty vesicles, as well as vesicles encapsulating GFP, in Tris-Cl buffer
 * Successfully formed vesicles encapsulating GFP in homemade S30 E. coli cell extract
 * Attempting to enclose cell extract in vesicles to attain expression of reporter DNA constructs
 * Attempting to find suitable pore proteins to prolong vesicle and expression lifespan