Extended Data Fig. 6: Phosphorylation of Pol II CTD in vitro, and CTD partitioning in MED1-IDR droplets.

a, Western blot showing phosphorylation of Pol II CTD by CDK7. Equal amounts of non-phosphorylated and phosphorylated GFP–CTD52 (see Methods) were run on a 3–8% SDS–PAGE gel, and analysed by western blot using anti-GFP antibodies. Similar results were obtained in two biological replicates. For gel source data, see Supplementary Fig. 1. b, Western blot showing phosphorylation of Pol II CTD by CDK9. Similar results were obtained in two biological replicates. For gel source data, see Supplementary Fig. 1. c, Representative images of droplet experiments that measured incorporation of Pol II CTD into MED1-IDR droplets. Purified mCherry–MED1-IDR at 10 μM was mixed with 3.3 μM GFP, GFP–CTD52 or GFP–CTD52 phosphorylated with CDK7 or CDK9 in droplet-formation buffers with 125 mM NaCl and 16% Ficoll-400 or 10% PEG-8000. d, Partition ratios of GFP and GFP–CTD in MED1-IDR droplets, and partition ratios of mCherry–MED1-IDR from experiments depicted in c.