Fig. 3. The disordered PEST domain in PU.1 drives dimerization in the absence of DNA.

(A) Concentration-dependent changes in hydrodynamic and volumetric properties by DOSY NMR, intrinsic Trp fluorescence anisotropy, and high-precision densimetry of ΔN117 in 0.15 M Na⁺ at 25°C. Red curves represent fits of the data to a two-state monomer-dimer transition. (B) Representative zero-charge ESI mass spectra of ΔN117 at 13 and 840 μM total concentration, normalized to the height of the monomer (17 kDa) peak. The ratios of the integrated dimer-to-monomer intensities (molecular weight shown) were French-curved to guide the eye. (C) Far-UV CD spectra of ΔN117 and ΔN165 at 25 μM, plotted on a per-molecule basis to highlight the contribution of the N-terminal residues. (D) Concentration-dependent, per-residue spectra of ΔN117 and ΔN165 (left). Dimerization as revealed by singular value decomposition of the ΔN117 spectra and fitted to a two-state transition. (E) ¹H-¹⁵N HSQC of 400 μM ΔN117 and ΔN165 at 0.15 NaCl. Under these conditions, ΔN117 was predominantly dimeric and ΔN165 was monomeric. The assignments shown are for ΔN117. Inset: {¹H}¹⁵N-NOE for ΔN117 and ΔN165.