Split RNAP biosensors can detect Bcl-2 family PPIs in mammalian cells. (A) Vector system to test binary Bcl-2 split RNAP PPI detection system in mammalian cells using PPI driven GFP mRNA as the RNA output. (B) HEK293T cells cotransfected with the plasmids shown in (A). 30 h after transfection, the cells were analyzed for GFP expression by fluorescence microscopy. Interactions between tBID and Bcl-2, Mcl-1, Bcl-XL, and Bcl-W, are readily detected compared to control, while NOXA is much more selective for interaction with Mcl-1. (C) Quantification of (B) (error bars are ± s.e.m, n = 5). Student’s t-test; **P < 0.001. 100 μm scale bar shown.