Tombusviridae. Tombusviridae

Description of Tombusviridae 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 28-35 nm. Capsids appear round, or hexagonal in outline, or slightly angular. The capsid surface structure reveals a regular pattern with distinctive features (of granular appearance). The capsomer arrangement is clearly visible, or is not obvious. The capsid consists of 32 capsomers (virion composed of 180 protein subunits). Physicochemical and Physical Properties Virions have a buoyant density in CsCl of 1.28-1.346-1.36 g cm-3. There are 1 sedimenting component(s) found in purified preparations, or 2 sedimenting component(s) found in purified preparations. The sedimentation coefficient is 130-134.2-140 S20w. Isoelectric point pH is 3.9-4-4.1. A260/A280 ratio is 1.64. The thermal inactivation point (TIP) is at 75-85-90°C. The longevity in vitro (LIV) is 21-104.5-300 days. Although the titer is dependent on the host, the decimal exponent (DEX) of the dilution end point is usually around 4-5, or 6, or 7. The infectivity is retained when deproteinized with proteases; retained when deproteinized with phenol or detergent. Nucleic Acid The Mr of the genome constitutes 14-16.92-18% of the virion by weight. The genome is monopartite, only one particle size is recovered, or segmented; bipartite, segements are distributed among 2 particle types of linear, positive-sense, single-stranded RNA. 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, or subgenomic RNA and satellite RNA (occasionally), or nucleic acid of host origin and subgenomic mRNA. Virions may also contain defective RNA species arising from a deletion of full-length genomic RNA. The genome is sequenced, and complete sequence is about 4600-4702-4800 nucleotides long. The genome has a base ratio of 27.8-28.13-28.6 % guanine; 24.9-26.06-27 % adenine; 21.2-21.5-22 % cytosine; 23-25.13-26.3 % uracil. The 5'-end of the genome has a probably methylated nucleotide cap. The terminus is protected, however, the presence of a cap was demonstrated only in 74.0.2.0.004 carnation mottle virus, Genus 74.0.2. Carmovirus). Each virion contains a full length copy and defective interfering copies (are known to occur). Proteins Proteins constitute about 82-82.66-84% of the particle weight. The viral genome encodes structural proteins and non-structural proteins. Virions consist of 1 structural protein(s). Non-Structural Proteins: Virus-coded non-structural proteins have been isolated and 3 non-structural protein(s) are found. Lipids Lipids are not reported. Genome Organization and Replication By itself, genomic nucleic acid is infectious (and addition of a cap analogue to in vitro RNA transcripts enhances infectivity little or not at all). Transcription: Sub-genomic RNA is present in infected cells. The genome expression is based on RNA production which can be analyzed by the dsRNA patterns found in the infected tissues. Usually there are 3-3.5-4 virus specified dsRNA species found in infected cells. Size of largest virus specified dsRNA 4.7-4.716-4.733 kbp. 2nd largest 2.1-2.144-2.188 kbp. 3rd largest 0.9-0.918-0.936 kbp. 4th largest 0.62 kbp. 5th largest 0.499 kbp. Translation: The genome replicates in the cytoplasm. Virions may provide helper functions to dependent virus during replication. Virion acts as helper for a satellite RNA.