These promoter constructs come pre-packaged as ready-to-transduce, lentiviral particles. Each lentiviral vector carries the same green fluorescent protein (GFP) under the control of a promoter.
Cellecta's PromoterTest reporter constructs include a range of commonly used promoters. Simply transduce the GFP-expressing lentiviral constructs into your cell line and compare the GFP intensities from each different construct. The intensity of the resulting fluorescence, as measured by FACS, correlates with the expression level of GFP, with higher GFP intensity indicating stronger promoter activity.
With this customizable kit, you can now measure the relative expression level of multiple promoters by assessing promoter strength (Fig. 1) as well as sustained long-term expression (Fig. 2) to find an optimal promoter for virtually any mammalian cell line.

Fig. 1 Relative expression levels of GFP by CMV, mCMV, SSFV, E/CMV, EFS and RSV promoters in various cell lines. (Data normalized by average expression in a cell line.)

Fig. 2 FACS readout shows that EF1L sustained the highest expression in this Induced pluripotent Stem Cell (iPSC) line.