Extended Data Fig. 3: Putative flat NEC double-layer lattice.

a, b, c Orthogonal section through average volume of lattice shown in Fig. 1f. There is no density for the membrane bilayers due to the majority of particles having their six-fold symmetry aligned with the tomogram Z axis (and the missing wedge). A total of 1944 C6 symmetrised particles were included in the average. d, Tangential sections through the volume at 1.4 nm intervals. e, A slice through the raw tomogram indicating the position of the inner nuclear membranes relative to the lattice. The membrane is not visible around the majority of the lattice layer due to its orientation to the tomogram missing wedge. The approximate position of the outer nuclear membrane was inferred from the exclusion zone of cytosolic components (ribosomes, intermediate filaments, microtubules). f, Two NEC hexamers segmented from the spherical lattice (Fig. 5, here shown in yellow) were fitted into one repeating unit of the lattice. In this orientation, pUL31 would form the interface between the two lattice layers. g, h, i, j, The hexamer centres in the double-layer lattice (yellow) are spaced 2 nm further apart and are rotated by approximately 20° to the 6-2-6 axis compared to spherical NEC (blue) and flat lattice derived from the HSV-1 crystal structure (purple). k, Slice through several adjacent type-1 NR, with the lumen of one of these zippered by putative head-head interacting NEC (yellow). Inset shows an orthogonal slice through the centre of the highlighted area. l, Plotback of individual symmetry units (dodecamers). There is a slight curvature to the lattice with a break in the middle, presumably to accommodate the tighter curvature of the underlying nucleoplasmic reticulum membrane.