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Virions have
a complex construction and consist of an envelope, a nucleocapsid and a
matrix protein. During their life cycle, virions have an extracellular phase.
Virions are enveloped and mature naturally by budding through the membrane
of the host cell. Virions are spherical to pleomorphic; filamentous and
other forms are common and (60–)150–200 nanom in diameter; 1000–10000 nm
long.
The envelope has surface projections. These are
distinctive spikes (of hemagglutinin-neuraminidase (HN) and fusion (F)
glycoproteins) evenly covering the surface. They are spaced widely apart.
These are embedded in a lipid bilayer. They comprise hemagglutinin and
neuraminidase (HN), or hemagglutinin (H), or surface glycoproteins (GP) or
fusion proteins. Surface projections are homooligomers and form spike-like
projections of 8–12 nm long; spaced 6–10 nm apart. Capsid/nucleocapsid is
elongated and exhibits helical symmetry, and the nucleocapsid is filamentous. |
