RACK1 Sedimentation equilibrium experiments. (A) The figure shows the best fits of experimental data for 300 μg/mL of RACK1 (4 °C) at 12000, 15000, and 18000 rpm with the self-association methods (SedPhat program - Material and Methods). The random distribution of the residuals (bottom panel) indicates that the fit is satisfactory. Sedimentation equilibrium data of RACK1 agree with a monomer structure with 37.2 kDa in equilibrium with of dimers and tetramers (see Results and Discussion for details). (B) Sedimentation equilibrium interaction between RACK1 and KI-1/57(122-413) was tested at 300 μg/mL of both proteins at 12,000, 15,000, and 18,000 rpm and 4 °C. The data were fitted by self-association method (SedPhat program - Material and Methods) and resulted in random distribution of the residuals (bottom panel) which indicates that the fit is satisfactory. The fitting data suggest that RACK1 and Ki-1/57(122-413) interacts with an affinity constant of (1.5 ± 0.2) × 106 M-1.