Arteriviridae. Arteriviridae

Description of Arteriviridae adapted from ICTVdb Virion Properties Morphology Virions consist of an envelope and a nucleocapsid. Virus capsid is enveloped. Virions are spherical and measure 60 nm in diameter. The envelope has small projections that cover evenly the surface. Surface projections form ring-like subunits and patterns are 10-14 nm in size. Capsid/nucleocapsid is round and exhibits icosahedral symmetry. The nucleocapsid is isometric with a diameter of 35 nm. Projections are small, evenly dispersed over the surface giving it a rough appearance. . Incomplete particles are common. They are disintegrated particles (regularly observed in preparations that were not fixed before negative staining). Physicochemical and Physical Properties Virions have a buoyant density in CsCl of 1.17-1.2 g cm-3; sucrose of 1.13-1.17 g cm-3. There are 1 sedimenting component(s) found in purified preparations. The sedimentation coefficient is 200-230 S20w. Nucleic Acid The genome is not segmented and contains a single molecule of linear positive-sense, single-stranded RNA. The complete genome is 13000 nucleotides long. The genome has a guanine + cytosine content of 48-53 %. The 5'-end of the genome has a methylated nucleotide cap; cap sequence type is m7G5ppp5'GmpNp. The 3'-terminus has a poly (A) tract (that is about 50 nucleotides long). Each virion contains a longer than full length copy. Proteins The viral genome encodes structural proteins and non-structural proteins. Virions consist of at least 4 structural protein(s) located in the envelope, membrane, peplomers, and nucleocapsid. The viral envelope contains 3 integral membrane proteins. Structural Proteins: Envelope protein large glycoprotein (GL, has a molecular mass of 30000-45000 Da. Envelope protein has a function assigned; is a triple spanning, integral a membrane protein. During post-translational processing envelope protein modifications occur that include N- glycosylation and disulfide cross-linking (forming a heterodimer with M proteins and probably forming the cup-like structures observed on the virion surface). Envelope protein small glycoprotein (GS, has a molecular mass of 25000-30000 Da; is a class I integral a membrane protein (which is a minor virion component, during post-translational processing envelope protein modifications occur that include glycosylation. Envelope protein nonglycosylated membrane protein (M) has a molecular mass of 16000-20000 Da; is a membrane protein (which transverses the membrane three times and thus resembling the M protein of Coronavirus and Torovirus, during post-translational processing envelope protein modifications occur that include disulfide cross-linking (with protein GL). Nucleocapsid protein N; has a molecular mass of 12000-15000 Da. Non-Structural Proteins: The virus codes for an RNA-dependent RNA polymerase. In addition to the polymerase, the virus codes for enzymes such as transcriptase and replicase. Lipids Lipids are present and located in the envelope. Virions are composed of 10% lipids by weight. Genome Organization and Replication By itself, genomic nucleic acid is infectious. Transcription: The viral genome is transcribed by a viral RNA-dependent RNA polymerase.