Transformation of E. coli

In recent years several techniques have been described for the introduction of DNA molecules into Escherichia coli . These are based on the findings of Mandel and Higa (1 ), who demonstrated that incubation of cells with naked bacteriophage DNA in cold calcium chloride resulted in uptake of virus and that a transient heat shock of the mixture greatly enhanced the efficiency of transformation. Subsequently, this method was used to introduce a variety of circular and linear DNAs into strains of E. coli , and many variations in the technique have been described that are aimed at increasing the yield of transformants (or transfectants in the case of M13 bacteriophage).