Fig. 9. The 50 bp element is required for full DPP responsiveness in COS cells. Luciferase activity of the lab550 enhancer and two 3' deleted derivatives upon stimulation of DPP signaling in transfected COS-1 cells. The DPP response is expressed as -fold activation over the basal activity of each reporter plasmid alone, which is schematically represented as a bar with the nucleotide position of the deletion at the bottom of the graph (see the legend of Fig. 3 for details). Deletion of the 50 bp element reduced the induction of 1/394 (22-fold) compared to 1/444 (37-fold) in COS cells. The 50 bp element (a slightly extended version was put into the expression vector for cloning purposes) is induced 10-fold by the activated TKV receptor and the co-transfected Smad-expressing plasmids.