CLONING, SEQUENCING AND EXPRESSION OF THE S-PROTEIN GENE FROM 2 GEOGRAPHICALLY DISTINCT STRAINS OF CANINE CORONAVIRUS

The gene encoding the spike (S) protein from two geographically distin ct strains (American and British) of canine coronavirus (CCV) was clon ed and sequenced. The nucleotide sequence revealed open reading frames of 1443 or 1453 amino acids, respectively. Structural features includ e an N-terminal hydrophobic signal sequence, a hydrophilic cysteine-ri ch cluster near the C-terminus, two heptad repeats and 29 or 33 potent ial N-glycosylation sites. Pairwise comparisons of S amino acid sequen ces from these isolates with other CCV strains (Insavel and K378) reve aled that heterogeneity, found mostly in the form of conservative subs titutions, is distributed throughout the canine sequences. However, 5 variable regions could be identified. Similar analysis with feline, po rcine, murine, chicken and human coronavirus sequences revealed that t he canine sequences are much more closely related to the feline S prot ein sequence than to the porcine S protein sequences even though they are all from the same antigenic group. Moreover, the sequence similari ty between CCV isolates and the feline coronavirus, feline infectious peritonitis virus (FIPV) was comparable. Expression of the CCV or the transmissible gastroenteritis virus (TGEV) S gene using the vaccinia v irus system produced a protein of the expected size which could induce extensive syncytia formation in infected canine A72 cells.