The causative agent (TGEV) of
porcine transmissible gastroenteritis belongs to the Coronaviridae, a family of enveloped viruses with a positive, single-stranded
RNA genome. Important progress has recently been made concerning the molecular biology of TGEV. The research work of our group has been focused on two main aspects: genome structure and functional domains of the envelope
proteins. TGEV genomic
RNA is organised into seven regions. The sequence of six of them, i.e. the 3' most 8300
nucleotides, has been established from
cDNA clones. Three genes encoding the structural
proteins, the peplomer
protein E2, the transmembrane
protein E1 and the
nucleoprotein, have been identified. Additional open reading frames allowed for the prediction of four non-structural
polypeptides, the role of which remains to be discovered. The remaining part of the genome (estimated length 20 kb) is thought to encode the polymerase. Expression of TGEV genes involves the production of six subgenomic mRNAs, which together with the virion
RNA, form a 3' terminal nested set. The peplomer
glycoprotein E2 (220 kDa) is 1431 residues long and highly glycosylated. Several domains were identified, including a C-terminal anchoring region and at least four major antigenic sites, which cluster in the amino half part of the molecule. Two sites containing most of the critical neutralisation determinants are highly conserved among TGEV strains. The
glycoprotein E1 (29kDa) is mostly embedded in the membrane and plays a crucial role in the virion architecture. However, a short N-terminal domain protruding out of the particle mediates
complement-dependent neutralisation, and induces
alpha interferon synthesis, likely through a direct interaction with the lymphocyte membrane.