Nucleotide sequence of the glycoprotein S gene of bovine enteric coronavirus and comparison with the S proteins of two mouse hepatitis virus strains.

The gene encoding the spike glycoprotein (S) of bovine enteric coronavirus (BECV) was cloned and its complete sequence of 4092 nucleotides was determined. This sequence contained a single long open reading frame with a coding capacity of 1363 amino acids (Mr 150,747). The predicted protein had 19 N-glycosylation sites. A signal sequence comprising 17 amino acids was observed starting from the first methionine residue. A potential peptidase cleavage site was located between amino acids 763 and 767. These cleavage explain the maturation of the primary product of the S gene to S1 (Mr 104,692) and S2 (Mr 84,175) spike structural proteins. Two amphipathic alpha-helices (amino acids 1007 to 1077 and 1269 to 1294) which may constitute the 12 nm stalk of the viral spike were also observed; another alpha-helix (amino acids 1305 to 1335) may be involved in the anchorage of the spike in the viral membrane. Comparison of this protein sequence to the described homologous mouse hepatitis (MHV) strain A59 and MHV-JHM S protein sequences led us to suggest that MHV-A59 and MHV-JHM S genes could be derived from a deletion of the BECV S gene.