(a) Composite, hexameric Y-complex core constructed from the hub structure (Fig. 1) combined with previously published X-ray crystal structure fragments. Within Nup84, 4 helices were modeled computationally. (b) Composite S. cerevisiae Y-complex based on A), with S. cerevisiae sequences threaded onto existing homologous structures. Compared to the universally conserved hexameric Y-complex core shown in A), Seh1 (red) is an additional component found in many organisms, including yeast. (c) Composite H. sapiens Y-complex with H. sapiens sequences threaded onto existing homologous structures. Nup37 (blue) is another Y-complex component only found in a subset of eukaryotes, including humans12. (d) Space filling surface view of the composite, hexameric Y-complex viewed from the front. (e) Side view. (f) Tilted view.