Pairs of oligonucleotide primers used in PCR are often designed with restriction sites in their 5' regions. In many cases, the sites are different in the two primers. In this case, amplification generates a target fragment whose termini now carry new restriction sites that can be used for directional cloning into plasmid vectors. The purified fragment and the vector are digested with the appropriate restriction enzymes, ligated together, and transformed into E. coli. - [Read Cloning PCR Products by Addition of Restriction Sites to the Termini of Amplified DNA 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. - [Read Preparation and Transformation of Competent E. coli 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. - [Read 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. - [Read Preparation and Transformation of Competent E. Coli: "Ultra-Competent" Cells Protocol]