Figure 1. Evolvability, conservation and structural units of the nuclear pore complex. A schematic of the NPC is shown, with the cytoplasm at the top and nucleoplasm at the bottom. The nuclear envelope is drawn as two light gray lines. Units of the NPC are the core scaffold (blue), which are related to the protocoatomer complexes and act to deform membranes, the FG-repeat Nups (blue to red gradient), which act as the selectivity and gating activities, and the cytoplasmic fibrils and nuclear basket (blue to red gradient) which interface with cargo, chromatin, transcription and mRNA maturation pathways. The trans-membrane Nups are shown in red, reflecting our current understanding of significant variations in the identity of these Nups. The bar indicates low, intermediate and high conservation, as keyed by the blue to red gradient. Cargo is shown in gray to indicate the great variability and range in protein and RNA-protein complexes that interact with transport factors that are considerably well conserved in eukaryotes.