Amplification and expression of the type-specific S region of type I and II FCoV. (a) The alignment of the amino acid sequences of the putative RBD of S protein from type II FCoV and type I FCoV with the sequences from prototypic viral strains. The boxed nucleotides represent N-linked glycosylation sites. GenBank accession number: FCoV NTU2 (GenBank: DQ160294), FCoV KU-2 (GenBank: AB086881), FCoV UCD1 (GenBank: AB088222), FCoV Black (GenBank: EU186072), FCoV C1Je (GenBank: DQ848678), FCoV RM (GenBank: FJ938051), FCoV UU-2 (GenBank:FJ938060), FCoV NTU156 (GenBank: GQ152141), FCoV 79–1146 (GenBank: DQ010921), FCoV 79–1683 (GenBank: JN634064), FCoV DF-2 (GenBank: JQ408981), CCoV NTU336 (GenBank: GQ477367), CCoV CB05 (GenBank: DQ112226), CCoV 1–71 (GenBank: JQ404409) and TGEV Purdue (GenBank: DQ811789). (b) Sf-9 cells were infected with two r-viruses (rFCoV-I and rFCoV-II) at different MOI values, and the cells were harvested at different times post-infection. The putative RBD of S proteins (23 kDa in size) from type I and type II FCoV were confirmed by Western blotting using an anti-histidine mAb.