After incubation, a 50 µL of a 3X substrate solution (containing 30 µL NanoBRET Nano-Glo Substrate, 10 µL Extracellular NanoLuc inhibitor, and 4,960 µL of Opti-MEM) was added to each well. Plates were incubated for 2-3 minutes at room temperature, then donor emission (450 nm) and acceptor emission (at 610 nm) values were read using a GloMax Discover. For lytic mode, the following changes were made. 100x tracer concentration for CRBN was 13 µM, 100X tracer concentration for VHL was 25 µM, 75 µL of a 200,000 cell/mL solution was plated in white non-binding 96-well plates, and 10 µL of a 10x digitonin solution was added immediately after the cells were treated with PROTACs. Plates were incubated in darkness for 5 minutes after digitonin addition to allow for permeabilization. 50 µL of 3X substrate (30 µL NanoBRET Nano-Glo substrate and 4,970 µL Opti-MEM) was added to each well and plates were incubated for 1 minute at room temperature before being read on a GloMax Discover as above. Western blotting analysis of dose-response degradation assay. Total protein quantity was determined using the BCA protein assay. Protein concentration was determined using the BCA assay. Samples were then prepared in LDS buffer and subsequently loaded onto NuPAGE TM 4-12% Bis-Tris Midi gels, followed by the transfer of the proteins onto nitrocellulose membranes. The membranes were blocked for 1 hour prior to incubation with the primary antibodies using 5% Milk TBST. Membranes were incubated at 4°C in either BRD4(Ab128874), BRD3(Ab50818) or BRD2(Ab139690) primary antibody overnight. Following overnight incubation, the membranes were incubated with complimentary IRDye® 800CW secondary antibodies and a hFAB™ Rhodamine Anti-Tubulin Primary Antibody (loading control) for 1 h and then imaged with a Bio-Rad imager. All western blots were analysed for band intensities using Image Lab (Bio-Rad). The data extracted from these blots were then plotted and analysed using . All western blotting figures were developed in Adobe Illustrator.