Table S1.

Rotational and translational diffusion of Ddx4

Protein	Concentration	MW(kDa)	D(cm2/s)*	RH†	$<$${{\mathrm{S}}^2}_{{\tau }_c}$$>$‡ (ns)
Ubiquitin§		8.5	2.0 × 10−6 ($\pm$0.1)	15.7	3.3
${\text{Ddx4}}_{dil}$	7 mg/mL¶	25.8	8.8 × 10−7 ($\pm$0.2)	31.6	1.5($\pm$0.5)
${\text{Ddx4}}_{14FtoA}$	${\text{D}}_0$#	24.8	9.0 × 10−7 ($\pm$0.1)	30.9	‖
${\text{Ddx4}}_{14FtoA}$	250 mg/mL	24.8	3.5 × 10−8 ($\pm$0.1)	**	2.4($\pm$0.8)
${\text{Ddx4}}_{14FtoA}$	370 mg/mL	24.8	9.2 × 10−9 ($\pm$0.9)	**	4.8($\pm$1.5)
${\text{Ddx4}}_{cond}$	380 mg/mL	25.8	7.5 × 10−9 ($\pm$0.4)	**	8.5($\pm$3)
${\text{Ddx4}}_{cond}$††	440 mg/mL	25.8	5.4 × 10−9 ($\pm$0.4)	**	10.4($\pm$4)

D₀, concentration extrapolated to 0; MW, molecular mass.

^*Measured by pulsed field gradient NMR as described in SI Materials and Methods (30 °C).

^†Hydrodynamic radius (RH) calculated from measured diffusion coefficient in buffer along with diffusion of acetate (30 °C) (SI Materials and Methods).

^‡Product of square of order parameter for backbone amide, S², and residue-specific overall tumbling time, τ_C, averaged over residues for which data is available (30 °C).

^§$<{{\mathrm{S}}^2}_{{\tau }_c}>$ data from refs. 57 and 58.

^¶Sample obtained from the dilute phase of phase-separated Ddx4

^#Extrapolated from self-diffusion data as a function of concentration to zero concentration.

^‖Relaxation data not measured.

^**Hydrodynamic radius cannot be accurately extracted from diffusion measurements on concentrated samples because of elevated viscosity. All estimates of R_H make use of dilute Ddx4 samples.

^††A lower NaCl concentration was used (7.5 mM) relative to all other Ddx4 samples to achieve a higher protein concentration in the condensed phase.