Over expression of an Enzyme Function in a Host

DNA and competent cells are mixed and incubated on ice for 15-30 min to allow the DNA to be taken up. The mixture is then heat-shocked at 42 °C for 1-2 min, which induces DNA repair enzymes, allowing the cells to recover from the competent state and DNA uptake. Recovery is allowed to occur in growth medium at 37 °C before streaking on an agar plate with appropriate selection. The plates are incubated at 37 °C overnight if successful, several colonies are formed. 

Transfection, DNA uptake in eukaryotic systems, often is more problematic then bacterial transformation the mode of DNA uptake is poorly understood and efficiency is much lower. In yeast, cell walls can be digested with degradative enzymes to yield fragile protoplasts, which are then able to take up DNA. Cell walls are resynthesized after removal of the degrading enzymes. Mammalian cells take up DNA after precipitation onto their surface with calcium phosphate [Fugene 6 (Roche) Lipofectin (Life Technologies) Effectene (Qiagen)]. Electroporation is often more efficient for transfection in eukaryotic cell systems, especially in yeasts. 

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