Virion is bullet-shaped: vesicular stomatitis virus
 

Virions of vesicular stomatitis virus are bullet-shaped because they contain two nested, left-handed protein helices.

     
  "Vesicular stomatitis virus (VSV)  is a bullet-shaped rhabdovirus and a  model system of negative-strand RNA viruses.  Through direct visualization by means of  cryo–electron microscopy, we show that each virion contains  two nested, left-handed helices: an outer helix of  matrix protein M and an inner helix of nucleoprotein N  and RNA. M has a hub domain with four contact sites that link to  neighboring M and N subunits, providing rigidity by clamping adjacent  turns of the nucleocapsid. Side-by-side  interactions between neighboring N subunits are critical for the  nucleocapsid to form a bullet shape, and structure-based  mutagenesis results support this description. Together,  our data suggest a mechanism of VSV assembly in  which the nucleocapsid spirals from the tip  to become the helical trunk, both subsequently  framed and rigidified by the M layer." (Ge et al. 2010:689)

  Learn more about this functional adaptation.