Team:UCL London/Approach

Protein Expression

E.coli is essentially one of the most widely applied in-vivo expression. The reason for its wide application is the fact that it is so well developed and the genome of the e.coli is is fully developmed and well understood. In biotechnology, as an example, a DNA sequence for a protein of interest could be into a high copy-number plasmid containing the lac promoter, which is then transformed into the bacterium Escherichia coli. Addition of IPTG (a lactose analog) activates the lac promoter and causes the bacteria to express the protein of interest.

One technique of insuring high levels of a protein is to clone the gene downstream of a well-characterized regulated promoter. In our case, we will be using pTAC, the tac promoter, a very widely used expression system. Being the strong hyprid promoter it is, it is repressed by the LacI protein, and on addition of IPTG, the lacI repressser is inactivated. This inactivtation breaks the strong repression of pTAC resulting in expression of pTAC. It has been shown that high expressions of pTAC is directly proportional to the concentration of IPTG added. And so by varying the concentratrion of IPTG added, you can regulate the rate of the expression of the desired protein downstream.