Most released viruses in the periphery of infected cells appeared as straight filaments in 3D reconstructions ( Figure 2F ). Some filamentous viruses displayed one bent or buckled end giving rise to hooked or six-shaped particles ( Figure 2G and Video S1). Filamentous viruses were on average 789 nm long and had a diameter of 88 nm (Table 2 ), in agreement with previous studies [20, 24] . All virions had a membrane envelope and contained a rod-shaped NC that displayed the regular striated pattern previously described [12, 20] . The volume between membrane envelope and NC was filled with a densely stained material, most likely the VP40 matrix protein, which appeared to link the envelope to the NC on all sides and along the whole length ( Figure 2F ). 3D analysis revealed that NCs in all released virions had the same length, on average 735 nm, and appeared bent or kinked when particles were hooked or six-shaped ( Figure 2G , Table 2 ). These length averages exclude a single outlier, which was a double-length filamentous virus with a double-length NC ( Table 2 ). The presence of NCs of the same length in the cytoplasm, at the PM, in filopodia, in all budding structures and in filamentous viruses suggests that the NC assembles into a helix of a defined and final length prior to being transported to the PM.