Tymoviridae. Tymoviridae

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. A260/A280 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.