Molecular Aspects of the Relationship of Transmissible Gastroenteritis Virus (TGEV) with Porcine Respiratory Coronavirus (PRCV)
Transmissible gastroenteritis, caused by a Coronavirus (TGEV), has been recognised as a viral disease since 1946 when the virus was first isolated by Doyle and Hutchings (1). TGEV has been shown to cause diarrhoea in pigs of all ages but has a high mortality, often 100%, in neonatal piglets. The TGEV virion, like all coronaviruses, contains an envelope, whose lipids are derived from the host cell endoplasmic reticulum, a single-stranded RNA genome, of positive polarity, and three structural proteins. The virion proteins are: a surface glycoprotein (peplomer) of Mr 200000, a glycosylated integral membrane protein observed as a series of polypeptides of Mr 28000–31000 and a basic phosphorylated protein (nucleoprotein) of Mr 47000 associated with the viral genomic RNA (2). Like all the coronaviruses the TGEV proteins are expressed from a series of subgenomic mRNA species, six in the case of TGEV (3), which have common 3′ ends but different 5′ extensions. The region of each mRNA responsible for the expression of a protein appears to correspond to the 5′-terminal region, often referred to as the ‘unique’ region, that is absent from the preceding smaller species. The TGEV genome encompassing the structural protein genes has been cloned and sequenced from a virulent British isolate, FS772/70 (4, 5, 6, 7, 8 and unpublished results), and from the avirulent Purdue strain (9, 10, 11, 12, 13, 14). This has led to the identification of five other potential genes, one of which appears to be the polymerase gene (8), another that appears to be located in the host cell nucleus and not in TGEV virions (8, 15) and three others whose products have yet to be identified in TGEV infected cells.
KeywordsIntegral Membrane Protein Porcine Epidemic Diarrhoea Virus Feline Infectious Peritonitis Neonatal Piglet Transmissible Gastroenteritis Virus
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