pcDNA™5/FRT/TO TOPO™ TA Expression Kit - FAQs

Use irreversible integration (Jump-In system) if the transgene should be sustained in the mammalian genome for a long time. Use reversible integration such as Flp-In system if the transgene needs to be replaced with another gene of interest after a short period of time.

The Jump-In system is PhiC31-integrase mediated and is a stable, targeted, and irreversible mammalian expression system, involving one integration step. The Jump-In TI (Targeted Integration) system needs two integration steps, both of which are targeted and irreversible. In contrast, the Flp-In system is a stable, targeted mammalian expression system that is reversible. The first integration is random (integration of pFRT/lacZeo) and the second integration (integration of the Flp-In expression vector) is targeted but reversible.

We have observed in-house that in cells where the FRT site has integrated into a very transcriptionally active locus in the host cell genome (seen more commonly in Flp-In CHO and Flp-In 293 cells but can also happen in Flp-In 3T3 cells and any other Flp-In host cell line), there is some "read-through" transcription and translation of the lacZ-Zeocin ORF post Flp-In recombination, even though the lacZ-Zeocin ORF does not have a bona fide promoter and ATG. In such cases, the hygromycin-resistant clones would also be lacZ positive and Zeocinantibiotic-resistant. To make sure that the integration is FRT site-specific and not random, we recommend doing a parallel control transfection with no pOG44 present. This should yield no surviving clones upon hygromycin selection, indicating that all the hygromycin-resistant clones obtained in the presence of pOG44 are indeed Flp recombinase-dependent and hence have the gene of interest integrated at the FRT site. Also, a Southern blot analysis of these clones will help verify that they do indeed have proper FRT integration of the gene of interest despite the expression of lacZ (although this is typically not necessary). Post Flp-Inrecombination, as long as you see hygromycin-resistant clones, we recommend that you select them and assay them for expression of your gene of interest.

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

In addition to the CAAT and TATA boxes, the CMV promoter in pcDNA3.1 vector contains sequence homologous to base pairs 137 to 724 of the sequence submitted by Boshart, et al (GenBank Accession # K03104). The complete enhancer region is contained between 214 and 620 of this sequence. Therefore, by this definition, the CMV promoter could be said to be "complete".

Please note that this promoter does not contain an intron. Some people believe that the complete promoter must contain the intron, but that has not been demonstrated to be necessary for expression.

There is no intron in the BGH polyA sequence. The BGH polyA signal (bases 1028-1252 in pcDNA3.1 vector) is the sequence that allows for polyadenylation of the RNA transcript. It is described in the following reference: The 3'-flanking sequence of the bovine growth hormone gene contains novel elements required for efficient and accurate polyadenylation. J Biol Chem.1992 Aug 15;267(23):16330-4

The reference states that the 3' untranslated region leading up to the poly adenylation core sequence (AATAAA) contains unique disperse non-consensus elements (consensus elements are poly U and GU-rich tracts) that serve to increase the efficiency of polyadenylation to a high degree, and that a 9-base sequence downstream of the core sequence facilitates efficient cleavage of the RNA strand. This leads to more stable and higher-abundance transcripts.