Figure 3.

(A) Scheme for obtaining dimerizer-dependent Fas activation. The fusion construct used consists of a myristoylation sequence for membrane anchoring, followed by two FKBP12 domains and amino acids 175–304 of human Fas, which includes the cell-killing domain (20). Addition of dimerizer is presumed to induce clustering of multiple Fas death domains, thereby activating the Fas-mediated apoptotic pathway. The presence of two FKBP domains on each protein may enable clustering of more than two death domains. (B) Dimerizer-induced killing of cells expressing the dimerizer-dependent Fas construct. M45-11, a clone of HT1080 cells that is stably transduced with the retrovirus pSRα–myristoylation–2FKBP-Fas-E, was treated overnight with the concentration of dimerizer shown, and viability was then measured. Values shown are the means of triplicate wells.