Fig. 2.

Comparison of the model predictions with the experimental data. (A) Experimentally measured flux as a function of concentration. Gray: Flux of the (NTR) Transportin through the NPC (normalized by the value at 1 μM Transportin concentration). Adapted from ref. 31. Black: Flux (normalized by the value at 1 μM) of NLS-GFP cargoes transported primarily by Kap 123p (an NTR) into the nucleus in live cells. Adapted from ref. 32. Both experiments show no obvious saturation of the flux into the nucleus toward a maximal value as the NTR concentration increases. (B) Single-molecule data depicting translocation probabilities which increase and transport/interaction times (SI Appendix, Text for definitions), which decrease with increased crowding; adapted from ref. 27. (C) Calculated flux (normalized by the value at 1 μM NTR concentration) into the nucleus as a function of NTR concentration within the cytoplasm. Flux appears to increase linearly with NTR concentration, with no saturation even at very high concentrations. Black: Fluxes measured from simulations; error bars indicate 1 SE. Red (solid): Analytical approximation using the dimensionally reduced 1D Fokker–Planck Equation diffusion model; SI Appendix, Text and Eq. 6; red (dashed): the alternative approximation using Eq. 7. The inset shows the same data plotted on linear axes. (D) Simulated translocation probabilities (blue triangles) and transport/interaction times (red crosses/gray squares) as functions of the NTR concentration outside the pore. The blue-shaded region indicates the regime where translocation probabilities increase and transport times decrease with crowding. Error bars indicate 1 SE. The simulation data can be explained using a dimensionally reduced 1D Fokker–Planck Equation diffusion model (solid lines); SI Appendix, Text and Eq. 6.