Herpesviruses

Herpesviruses

	Herpesviruses - The herpesviruses are found in a wide variety of hosts and tissues, but have a common morphology. They cause a number of infections in humans and other vertebrates. The herpesviruses are large (140.170 nm) viruses. The capsid is enclosed in a glycoprotein lipid envelope about 30 nm thick. The thickness of the membrane indicates that either there is a matrix between the nucleocapsid and the envelope, or that the membrane has an unusual structure, The membrane has surface projections or spikes
The spherical nucleocapsid is about 100 nm in diameter, with a. dense central core of dsDNA. The capsid consists of 162 hollow, columnar capsomeres arranged in a 5:3:2 symmetry, (T=16) to form an icosahedron. There are 12 pentamer capsomeres at the apices and 150 hexamer capsomeres at the faces or edges. The genome consists of linear dsDNA. When double stranded molecules are digested slightly from either 3' or 5' ends, circular DNA molecules are produced, indicating terminal redundancy (repetition).Electron microscope observations have shown that some DNA molecules have two loop-and-stem structures, indicating repetitive segments.
Fragmentation experiments with restriction endonucleases indicate that the DNA consists of one long and one short DNA molecule covalently and randomly joined at the junction of their identical regions. Replication may take place independently, or there may be recombination producing four different orientations of the genome. The mature virus has 24 proteins of which at least 12 are glycoproteins. Four proteins have been found in empty capsids, of which p5 is the major capsid protein. Viral protein synthesis bikes place in three groups, non structural proteins, minor structural proteins and major structural proteins
Polyamines are sufficient to, neutralize 50% of the DNA phospholipids. Spermine is found in the nucleocapsid rand spermidine and protein kinase in the outer envelope. When the herpesvirus enters the host cell the outer envelope is removed in the cytoplasm . The nucleocapsid migrates to the nucleus. Messenger RNA is synthesized and transported to the cytoplasm, where viral proteins are synthesized. They then migrate to the nucleus where replication of viral DNA takes place and the proteins are assembled

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