Preparation and Transformation of Competent E. coli Protocol Procedure generates competent cultures of E. coli that can be transformed at high frequencies (5 x 108 transformed colonies/µg of superhelical plasmid DNA). IMPORTANT All steps in this protocol should be carried out aseptically.
Preparation and Transformation of Competent E. Coli: "Ultra-Competent" Cells Protocol Protocol reproducibly generates competent cultures of E. coli that yield 1 x 108 to 3 x 108 transformed colonies/µg of plasmid DNA. The protocol works optimally when the bacterial culture is grown at 18°C. If a suitable incubator is not available, a standard bacterial shaker can be set up in a 4°C cold room and regulated to 18°C.