E) Substitution of all arginines in hnRNPA2 LC with lysine prevents the partitioning of hnRNPF PLD into hnRNPA2 LCRK droplets. Removing all charged residues except for arginine from hnRNPA2 LC (hnRNPA2 LCCD,R) allows partitioning of hnRNPF PLD into droplets, indicating arginine in hnRNPA2 LC is required and necessary for hnRNPF partitioning. hnRNPA2 LCRK does not phase separate much as hnRNPA2 LC at these conditions, see Figure S1J for quantification of phase separation of variants. Conditions: 20 µM proteins, 20 mM MES pH 5.5 50 mM NaCl, 150 mM urea. Scale bar: 10 µm. 