Coronaviridae

Abstract

The family Coronaviridae comprises a monogeneric group of 11 viruses which infect vertebrates. The main characteristics of the member viruses are: (i) Morphological: Enveloped pleomorphic particles typically 100 nm in diameter (range 60-220 nm), bearing about 20 nm long club-shaped surface projections. (ii) Structural: A single-stranded infectious molecule of genomic RNA of about (5-7) X 10(6) molecular weight. A phosphorylated nucleocapsid protein [mol. wt. (50-60) X 10(3)] complexed with the genome as a helical ribonucleoprotein; a surface (peplomer) protein, associated with one or two glycosylated polypeptides [mol. wt. (90-180) X 10(3)]; a transmembrane (matrix) protein, associated with one polypeptide which may be glycosylated to different degrees [mol. wt. (20-35) X 10(3)]. (iii) Replicative: Production in infected cells of multiple 3' coterminal subgenomic mRNAs extending for different lengths in the 5' direction. Virions bud intracytoplasmically. (iv) Antigenic: 3 major antigens, each corresponding to one class of virion protein. (v) Biological: Predominantly restricted to infection of natural vertebrate hosts by horizontal transmission via the fecal/oral route. Responsible main for respiratory and gastrointestinal disorders.

Fig. 1

Structure and expression of the MHV genome. The size and structural relationships of the MHV intracellular mRNAs arc shown. No difference between the genome RNA and mRNA 1 has yet been described. Each mRNA encodes only one protein, and the translation products of mRNAs 7, 6 and 3 have been identified as the intracellular precursors to the virion nucleocapsid, matrix and peplomer proteins, respectively. As the size of the translation product for each mRNA corresponds approximately to the coding potential of the 5′ sequences which are absent from the next smallest mRNA, it seems likely that only these regions are translated into protein.