Description of Filoviridae
adapted from
ICTVdb
Virion Properties
Morphology
Virions consist of an
envelope, a nucleocapsid, a polymerase complex, and a matrix
protein. Virus capsid is enveloped. Virions are filamentous, or
pleomorphic, flexible with extensive branching. U- or 6-shaped
and circular forms occur particularly after purification. Virions
measure about 80 nm in diameter; greatly variable up to 1400 nm
in length, or 790-970 nm in length (after purification). Surface
projections are spaced widely apart, distinctive knob-shaped
peplomers that cover evenly the surface and are embedded in a
lipid bilayer. Surface projections are composed of one type of
glycoproteins (GP), are 10 nm long and spaced 10 nm apart.
Capsid/nucleocapsid is elongated and exhibits helical symmetry.
The nucleocapsid is helical; is cross-striated and a width of 50
nm. Axial canal is distinct and 20 nm in diameter. Basic helix is
obvious. Pitch of helix is 5 nm.
Physicochemical and Physical Properties
The molecular mass (Mr) of
virions is 382 x 10
6. Virions have a buoyant density
in CsCl of 1.32 g cm
-3 (for nucleocapsids). The
density of virions is 1.14 g cm
-3 (in potassium
tartrate gradient). The sedimentation coefficient is 1.4
S20w (for longer particles it is very high).
The thermal inactivation point (TIP) is at about 60°C (after
30 min). Under
in vitro conditions virions are relatively
stable when stored at 15°C to 20°C; sensitivecanal is
distinct; acid environment of pH 5 (hypochlorite, sensitivecanal
is distinct; alkaline environment of pH 8 (quaternary ammonium
salt). Virions are sensitive to treatment with lipid solvents,
phenol (phenolic disinfectants), formaldehyde, and
ß-propiolactone. The infectivity is reduced after exposure
to irradiation (UV and gamma irradiation).
Nucleic Acid
The Mr of the genome constitutes 1.1% of the virion
by weight. The genome is not segmented and contains a single
molecule of linear negative-sense, single-stranded RNA. The
complete genome is 18900-19000 nucleotides long. The RNA is
sequenced, but only an estimate is available, complete sequence
is 18900-19000 nucleotides long. Nucleotide sequences at the
3'-terminus are complementary to similar regions on the 5' end.
The 5'-end of the negative-sense strand does not have a
covalently attached terminal protein; genome does not have cap.
The 3'-terminus has conserved nucleotide sequences (leader, in
genera of same family. The 3'-terminus has no poly (A) tract.
Proteins
The viral genome encodes structural
proteins and non-structural proteins. Virions consist of 5
structural protein(s) located in the envelope (surface
glycoprotein), nucleocapsid (NP), polymerase complex
(transcriptase-polymerase component and RNA-dependent RNA
transcriptase-polymerase), matrix.
Structural Proteins: Envelope protein GP has a
molecular mass of 74500-74800 Da. Envelope protein has a function
assigned; is a glycoprotein and forming the viral spikes (in the
form of trimers, during post-translational processing envelope
protein modifications occur that include glycosylation (of the
first small ORF yielding a soluble small glycoprotein sGP, not
observed in Marburg virus). Nucleocapsid protein NP has a
molecular mass of 77900-83300 Da; is binding to the genomic RNA.
Nucleocapsid protein VP30; has a molecular mass of 29700-31500
Da. Matrix protein VP40; has a molecular mass of 31700-35800 Da.
Matrix protein is a transmembrane protein, or a
membrane-associated protein. Matrix protein VP24; has a molecular
mass of 28300-28800 Da. Matrix protein is presumably
transmembrane protein, or membrane-associated protein.
Lipids
Lipids are present and located in the
envelope. The composition of viral lipids and host cell membranes
are similar.
Genome Organization and Replication
By itself, genomic nucleic acid is not infectious.