Cells were seeded onto 8-chamber coverglass (Nunc™ Lab-Tek™ II Chambered Coverglass, 155409) coated with 5 μg/ml laminin (BioLamina LN511), in 2i media and appropriate drugs. For all experiments, cells were grown overnight in the chambers. Protein degradation was induced by treating cells with a final concentration of 400 μM dTAG-13 (Sigma SML2601) for 2 hrs or 6 hrs (2 hrs: Sox2, Taf1, Tbp/Trf2, Gtf2f1, CDK7; 6 hrs: Rad21 and Med19). 0.04% v/v DMSO was used as control. Before imaging, cells were labeled with the relevant Halo-dye (Promega, Janelia Fluor® HaloTag® Ligands) or SNAP-dye (SNAP-Cell® 647-SiR, NEB S9102S) with media containing 0.3 μM dye for 10 min, at 37°C, followed by three times rinsing with new media. Rpb1 protein degradation was induced by treating cells with 40 nM Halo-PROTAC-E(34 (link)) for 2 hrs and 5 nM Halo-dye for 1 hr. For THZ1 and Triptolide treatment, cells were treated by 100 nM for 1hr. For combined dTAG and inhibitor treatment, cells were treated by dTAG-13 for 6 hrs and 100 nM inhibitor for 1hr.