Description of Tymoviridae
adapted from
ICTVdb
Virion Properties
Morphology
Virions consist of a
capsid. Virus capsid is not enveloped, round with icosahedral
symmetry (T=3). The capsid is isometric and has a diameter of
25-28-33 nm. Capsids appear round, or hexagonal in outline. The
capsomer arrangement is clearly visible, or is not obvious. The
capsid consists of 32 capsomers; 12 of which are pentons; 20 are
hexons.
Physicochemical and Physical Properties
Virions have a buoyant density in
CsCl of 1.26-1.46 g cm
-3. There are 2-3 sedimenting
component(s) found in purified preparations. The sedimentation
coefficient is 106-125
S20w, or 119-120
S20w; of the other(s) are 42-64
S20w, or 54-57
S20w.
Isoelectric point pH is 3.3-9.46. A
260/A
280
ratio is 0.64-8.51, or 0.87-1.63. The thermal inactivation point
(TIP) is at 55-90°C, or 60-70°C. The longevity
in
vitro (LIV) is 2-100 days, or 3-32 days. Although the titer
is dependent on the host, the decimal exponent (DEX) of the
dilution end point is usually around 2-9, or 5. The infectivity
is not changed by treatment with ether; retained when
deproteinized with proteases; retained when deproteinized with
phenol or detergent.
Nucleic Acid
The Mr of the genome constitutes 23-39% of the
virion by weight. The genome is monopartite. Only one particle
size of linear, positive-sense, single-stranded RNA is recovered.
Minor species of non-genomic nucleic acid are also found in
virions, or not found in virions. The encapsidated nucleic acid
is mainly of genomic origin, but virions may also contain
subgenomic RNA, that is mRNA. The complete genome is 6000-7600
nucleotides long. Genome is sequenced, but only an estimate is
available, complete sequence is 6000-7600 nucleotides long. The
genome has a base ratio of 13.6-20.5 % guanine; 17-24.1 %
adenine; 31.3-41 % cytosine, or 50 % cytosine; 22.15-29.4 %
uracil. The 5'-end of the genome has a methylated nucleotide cap;
cap sequence type is m7G5'ppp5. The 3'-terminus has a subgenomic
promoter, a conserved region known as "tymobox", or no subgenomic
promoter region. The 3'-terminus has a tRNA-like structure, or no
tRNA-like structure. The genome has an intergenic poly (A) region
at 3' terminal poly A tract.
Proteins
Proteins constitute about 61-77% of
the particle weight.
The viral genome encodes structural proteins and
non-structural proteins. Virions consist of 1 or 2 structural
proteins located in the capsid.
Structural Proteins: Capsid protein has a
molecular mass of 20000-28000 Da; is the coat protein.
Non-Structural Proteins: Virus-coded
non-structural proteins have been identified by sequence analysis
and 2 non-structural protein(s) are found.