Viruses Cytoplasmic alterations

All enveloped human viruses acquire their phospholipid coating by budding through cellular membranes. For example, with the influenza virus, the capsid protein subunits are transported from the ribosomes to the nucleus, where they combine with new viral RNA molecules and are assembled into the helical capsids. The haemagglutinin and neuraminidase proteins that project from the envelope of the normal particles migrate to the cytoplasmic membrane where they displace the normal cell membrane proteins. The assembled nucleocapsids finally pass out from the nucleus, and as they impinge on the altered cytoplasmic membrane they cause it to bulge and bud off completed enveloped particles from the cell. 

It has been known for some time that infection with various types of viruses impairs the permeability barrier function of the host cell cytoplasmic membrane, allowing ordinarily impermeable large molecules to enter the cell from the surrounding medium and allowing particulate intracellular material to leak out. A good example of this is penetration of supravital dyes, such as trypan blue, to enter cells, usually late after viral infection as a criterion of cell death. In addition, certain viral infections induce earlier and more subtle changes by altering membrane transport of small ions into or out of the infected cell. A few selected examples of altered membrane permeability of the cytoplasmic membrane are cited here as an example of readily measured cytopathic effects of well-known virulent viruses. 

Alterations in the permeability of the plasma membrane after infection cause not only changes in the ionic composition of the cytoplasm but also affect the distribution of other small metabolites (Condit, 1975 Ponta et al., 1976 Carrasco, 1977). Carrasco (1978) observed that the membrane of SF virus-infected cells became permeable to Gpp CH2P, a nucleotide analogue that inhibits protein synthesis in vitro, at the onset of viral protein synthesis and that inhibition in vivo by Gpp CH2P was specific for infected cells. 

---