pcDNA™3.4 TOPO™ TA Cloning Kit

We do not recommend storing competent E. coli strains in liquid nitrogen as the extreme temperature can be harmful to the cells. Also, the plastic storage vials are not intended to withstand the extreme temperature and may crack or break.

We recommend storing our competent E. coli strains at -80°C. Storage at warmer temperatures, even for a brief period of time, will significantly decrease transformation efficiency.

Other 293 cell lines may be used with the Expi293 Expression System. However, before these cell lines may be used for transfection studies, they must be adapted to serum-free, suspension culture in Expi293 Expression Medium and evaluated for transfection and expression.

Find additional tips, troubleshooting help, and resources within our Protein Expression Support Center.

pcDNA 3.4-TOPO TA vector is an improvement over pcDNA 3.3-TOPO TA vector. It contains the WPRE (Woodchuck Posttranscriptional Regulatory Element) that allows for 2- to 3-fold higher levels of expression than pcDNA 3.3-TOPO TA vector.

We recommend using the pcDNA 3.4-TOPO TA vector (Cat. No. A14697). This vector contains the native, full-length CMV promoter and a WPRE (Woodchuck Posttranscriptional Regulatory Element) downstream of the cloning site, both of which contribute to high level gene expression (about 2-3 fold higher expression than with pcDNA3.3 TOPO vector, which in turn provides 2-5 fold higher expression than with a standard pcDNA vector). Of course, the expression level is also protein-dependent.

Find additional tips, troubleshooting help, and resources within our Protein Expression Support Center.