Extended Data Fig. 2. The ProTα-H1 dimer is the dominant population in the dilute phase.

Single-molecule transfer efficiency histogram of ProTαC (labeled at position 56 and 110) in the dilute phase at 128 mM ionic strength (TEK buffer including 120 mM KCl). The phase-separated mixture was centrifuged, so that the dense phase coalesced into a single large droplet and no small droplets remained in the dilute phase. The dilute phase was aspirated and transferred into a sample chamber for single-molecule measurements. In the fit (lines), the centers of the Gaussian peak functions were constrained to the transfer efficiencies measured for unbound ProTα and the ProTα-H1 dimer (Fig. 2f) to within experimental uncertainty. The shaded peak near a transfer efficiency of zero originates from molecules lacking an active acceptor dye.