The VP40 matrix protein shows a regular 5 nm lattice spacing ( Figure 2B , C). Both the nucleocapsid and the VP40 layers are ordered, however the contacts between them appear to be nonsymmetrical ( Figure 2D ), implying some flexibility in their intermolecular contacts. It has been shown that VP35 interacts with the VP40 and can be packaged into VP40 VLPs [37] . The localization of the VP24-VP35 bridges on the periphery of the nucleocapsid, may allow interactions of one or more of the nucleocapsid proteins with VP40, possibly through projecting low-density protein loops. There is a 6-7 nm gap of low density between the nucleocapsid and the VP40 layer, but tomography also shows discrete areas of connectivity between the nucleocapsid and matrix protein layers, which may be connections between the envelope and the nucleocapsid ( Figure 3I ). These results are substantiated by the analysis of sub-tomograms where helical symmetry is clearly evident but was not imposed (Figures 4, S4) . The use of sub-tomogram analysis improves the resolution of the data by averaging sub-tomograms together which are at different angular orientations. The helical nucleocapsid is clearly identified in the structure, including the gap between the envelope-VP40, and the nucleocapsid-VP40. The right-handed pitch of the helix is clearly discernable (Figure 4E ), as well as the putative location of several VP40 proteins, although the resolution of the tomographic data by itself is slightly lower than with single particle analysis. While showing the overall organization of EBOV, tomography also allows estimation of the stoichiometry of the major structural proteins (Figure 3 , movie S2). Both EBOV and VP40-GP VLPs have an irregular distribution of the GP spikes on the surface (Figures 3, S3) demonstrating the lack of any ordered lattice-like arrangement with the matrix protein VP40. The spikes are clustered, and the average centre-to-centre spacing is 15.2 nm ( Figure S3, and movie S3) . We calculate that a virion of 982 nm in length would have about 1888 copies of the GP spike, and 8391 copies of VP40. The wide spacing of the EBOV GP in the viral envelope allows plenty of space for free access and binding of any neutralizing antibodies directed at both the club-shaped head and stem region without stearic hindrance (Figures 3J, S3) .