EF1-alpha promoter versions of the Tet-On 3G inducible expression system provide for consistent long-term expression of the Tet-On 3G transactivator, even in cell types known for their tendency to silence a CMV promoter over time, such as hematopoietic cells and stem cells. This means that in these cell types, long-term tetracycline-inducible expression can be achieved. The systems contain the same pTRE3G vectors as our standard Tet-On 3G systems that generate the lowest possible background expression; however, the Tet-On 3G transactivator is expressed from an EF1-alpha promoter instead of a CMV promoter. The EF-1 alpha promoter in these systems is derived from the human EEF1A1 gene that expresses the alpha subunit of eukaryotic elongation factor 1.

We tested the EF1-alpha version in Jurkat cells, a cell line known to show reduced expression and clonal variation in expression from CMV-based vectors. When expressing the Tet-On 3G transactivator protein from the EF1-alpha promoter, 83% of the Jurkat Tet-On 3G clones showed strong inducible expression and 33% demonstrated very high inducibility (greater than 2,000-fold). Such levels of control are not possible when using previous versions of the Tet-On system for this cell line.