Fig. 4.

Brushes collapse sparse layers do not. (A) Plot of Δd vs. ρ_Kapβ1, where the extent of collapse increases for taller cNup62 brushes (red > green > purple > grey) as compared to sparser layers (blue, pink). A greater amount of bound Kapβ1 is also required for taller brushes to recover before reaching pileup (red > green > purple > grey). Sparse cNup62 layers exhibit a negligible collapse followed by an immediate pileup without recovering (blue, pink). (B) Plot of the total (Kapβ1 and cNup62) mass-volume density change Δυ vs. relative height change Δd/d₂(initial). (1) For brushes (red, green, purple, grey), a linear increase in Δυ accompanies a 10% reduction in Δd/d₂(initial) because of cNup62 compaction upon collapse. Their overlap reveals that the total space occupied scales with the extent of collapse and is conserved. (2) The transition into recovery at Δυ of approximately 20 Da/nm³ proceeds with additional Kapβ1 binding without changing Δd/d₂(initial). Saturation at Δυ of approximately 70 Da/nm³ denotes FG domain reextension to maintain its capacity to accommodate more Kapβ1, marking the commencement of (3) pileup. Sparser conformations (blue, pink) have a low Kapβ1 capacity, and pile up at low Δυ without recovering.