Baculoviridae. Baculoviridae

Description of Baculoviridae adapted from ICTVdb Virion Properties Morphology Virions consist of an envelope and a nucleocapsid. During their life cycle, virions have an extracellular phase; can occur in two phenotypes. The infection is initiated by extracellular virions in the gut epithelium (phenotype I) and phenotype II virions generated when the nucleocapsids bud through the plasma membrane at the surface of infected cells (termed budded virions or BV). Virus may be sequestered within inclusion bodies that are occluded by protein bodies, or occluded by a crystalline protein matrix, or not occluded and typically contain one nucleocapsid composed of a single viral protein, polyhedrin, or granulin. Virus initiating infection is occluded by a crystalline protein matrix of polyhedral shape, or of ovicylindrical shape. Each occlusion body measures 0.13-15 µm and contains one virion, or several virions; virions in occlusions consist of a single nucleocapsid (S), or multiple nucleocapsids (M) within a single viral envelope. Virus capsid is enveloped. Virions are rod-shaped. A cell-associated virus, second phenotype, is generated when the nucleocapsid buds through the plasma membrane at the surface of infected cells. BVs typically contain a single nucleocapsid, or is needed if infection is not restricted to the gut epithelium cells. The secondary infected tissue produces occluded virions (ODV). Intracellular virions are enveloped with a loose fitting membrane. The envelope surrounds one nucleocapsid, or two nucleocapsids to several nucleocapsids; has terminal surface projections. Surface projections are peplomers. Surface projections are composed of one type of protein; projection proteins are glycosylated. Capsid/nucleocapsid is elongated with helical symmetry. The nucleocapsid is rod-shaped with a length with a length of 200-450 nm and a width of 30-100 nm. Capsid electron dense. Nucleic Acid The Mr of the genome constitutes 8-15% of the virion by weight. The genome is not segmented and contains a single molecule of circular, supercoiled, double-stranded DNA. The complete genome is 90000-230000 nucleotides long. Genome is sequenced, but only an estimate is available, complete sequence is 80000-180000 nucleotides long. The genome has a guanine + cytosine content of very variable and ranges from 28-59 %. Proteins Particles are made up of probably 12-20 proteins (however, genomic analyses suggest that 100-200 proteins may be encoded). The viral genome encodes structural proteins and non-structural proteins located in the envelope and capsid (only BV), envelope, capsid, and occlusion bodies (ODV). Lipids Lipids are present and located in the