FIG. 2.

Identification of a 22-kDa protein in MHV-infected DBT cells. (A) The schematic shows the location of the region of gene 1 used to express the protein against which the B4 antibodies were raised. The subclone extends from the XbaI site at nt 12303 to the KpnI site at nt 13906, and the expressed protein extends from aa 4032 to the end of ORF 1a (filled bar). (B) Immunoprecipitation of proteins from MHV-infected DBT cells. Cells were infected (lanes i) or mock infected (lanes m), and proteins were labeled and harvested as described in Materials and Methods. Proteins were immunoprecipitated with antibodies against whole MHV virions (αMHV), the SP9 antisera directed against 3CLpro, or the B4 antiserum. B4-pre indicates preimmune serum from the rabbit used to induce antibodies against the B4 protein. In lanes 4, 8, 9, and 10, proteins were labeled in the presence of the proteinase inhibitors leupeptin (lane L), phenylmethylsulfonyl fluoride (lane P), or E64d (lanes E). Mass markers (in kilodaltons) and the locations of the spike (S), nucleocapsid (N), and matrix proteins (M) are indicated to the left of the gel, and the locations of 3CLpro and other newly identified proteins are shown to the right of the gel.