In order to further investigate the nucleocapsid repeat identified in the 2D analysis the iterative helical real space reconstruction method (IHRSR) was implemented [26, 27] . This procedure requires an initial 3D helical reference structure which is used for image alignment. In this investigation a linear region of the Ebola virus which was extracted from a tomogram was used to generate this helical reference structure. This initial 3D structure was first pre-treated with a Gaussian mask to select only the nucleocapsid-containing region of the virus tomogram. An auto correlation function was then performed in which the volume was rotated around the helical axis, and translated along the axis of the nucleocapsid. At each rotational and translational position and autocorrelation value was calculated (between the shifted and unshifted volume). The net result of this process was the determination of the helical symmetry present in the tomogram. In order to analyse the data generated by this procedure the Microsoft excel spread sheet program was used. The correlation plots generated by this process solved the handedness, pitch, and number of repeats per turn for the nucleocapsid. These symmetry parameters were then applied to the tomogram to generate the initial 3D model. The IHRSR method was then applied to the 34,605 single particle images of the nucleocapsid as previously described [26, 27] .