Modeling of RNA in the Ebola nucleocapsid. Two previously determined atomic resolution structures of negative stranded RNA viruses (VSV (2GIC.pdb) [58] , and RSV (2WJ8.pdb) [32] ) were used to estimate the EBOV nucleocapsid length and number of nucleotides per nucleoprotein. Images of VSV (A) and RSV (B) are shown as a molecular surface with the protein in orange and the RNA as a green ribbon. From left to right, they show a surface view from the side, a side-on cross section, an end-on view, the RNA density alone in projection, and a rotational average of the projection. The VSV-based estimate, with a saw-tooth pattern of RNA in the helix, gave a nucleocapsid which 614.37 nm long, too short for the measured length of the G1 EBOV (982 nm). The RSV-based model, with a relatively straight/circular pattern of RNA in the helix predicted a nucleocapsid 914.55 nm long, which closely fits the measured length of G1 virions, after allowing ,34 nm space at each end to accommodate the curve of the envelope containing GP spikes and matrix proteins. The RSV-like model gives 13 nucleotides per nucleocapsid protein which is similar to previous biochemical estimates of 12-15 for Marburg virus [33] , suggesting that the RNA in the EBOV nucleocapsid is arranged in a smooth helical pattern at a diameter of ,22 nm. (TIF)