(A). Turbidity of tau187-RNA CC upon heating (Expt.1 ([tau], [NaCl]) = (50 μM, 120 mM), green dots; Expt.2 ([tau], [NaCl]) = (40 μM, 30 mM), purple dots). Absorbance at λ = 500 nm were normalized and used as turbidity value. Turbidity-temperature data of the heating curves were fitted with a sigmoidal function (solid line) as described in (Materials and methods), and the temperature at which normalized turbidity reaches 0.5 was assigned to cloud point, Tcp. (B)-(C). Experimental phase diagram (points) showing [tau] vs. Tcp and [NaCl] vs. Tcp along with the binodal curve generated from fitting the data to the FH-VO model with χ = χ(Tcp) (solid line). (D). Diagram of Flory Huggins lattice. Tau and RNA are represented by consecutively occupied lattice sites. (E). Each experimental condition in (A) was independently fit to the FH-VO model (solid lines) to obtain an empirical χ value. (E) shows two representative curves. These empirically determined values of χ are shown as points in (F). The solid line in (F) is a linear regression, generating χ = χ(Tcp), which is then used to generate the binodal lines in (B) and (C).