To ensure the successful assembly and subsequent transformation of assembled DNAs, NEB recommends the following:
DNA: PCR product purification is not necessary if the total volume of all PCR products is 20% or less of the assembly reaction volume. Higher volumes of PCR products may reduce the efficiency of high-fidelity DNA assembly and transformation due to the elevated carryover amounts of PCR reaction buffer and unused primers present in the PCR product. Column purification of PCR products may increase the efficiency of both high-fidelity DNA assembly and transformation by 2–10 fold and is highly recommended when performing assemblies of three or more PCR fragments or assembling longer than 5 kb fragments. Purified DNA for assembly can be dissolved in ddH2O (Milli-Q® water or equivalent is preferable), TE or other dilution buffers.
Insert: When directly assembling fragments into a cloning vector, the concentration of assembly fragments should be at least 2 times higher than the concentration of vector. For assembly of 4 or more fragments into a vector, we recommend using an equimolar ratio of fragments.
Transformation: NEB 5-alpha Competent E. coli (High Efficiency, NEB #C2987) provided with the NEBuilder HiFi DNA Assembly Cloning Kit are recommended for use for assembled products of less than 15kb. It is also possible to use other NEB competent E. coli strains, with the exception of BL21, BL21(DE3), Lemo21(DE3), Nico(DE3), and SHuffle®. When using competent E. coli from a vendor other than NEB, we have seen decreased robustness of transformation with high-fidelity DNA assembled products.
Electroporation: Electroporation can increase transformation efficiency by several logs. When using the NEBuilder HiFI DNA Assembly Master Mix, use 1μl of the assembled product for electroporation, and plate multiple dilutions.
Should you require the use of Electrocompetent cells, please use the "Electrocompetent Cells Transformation Protocol".
Biology: Some DNA structures, including inverted and tandem repeats, are selected against by E. coli. Some recombinant proteins are not well tolerated by E. coli and can result in poor transformation or small colonies.