Identification of two epitopes in the carboxyterminal 15 amino acids of the E1 glycoprotein of mouse hepatitis virus A59 by using hybrid proteins.

cDNA fragments coding for the carboxy terminus of the E1 envelope glycoprotein from mouse hepatitis virus A59, a coronavirus, were cloned into the bacterial expression vector pEX. Clones expressing E1 antigenic determinants were selected with a polyclonal anti-E1 antibody and used for immunization of rabbits and for affinity purification of existing polyclonal antisera. Immunofluorescence testing and immunoperoxidase labeling of coronavirus-infected cells showed that these reagents were monospecific for E1. In addition, by using hybrid proteins containing different lengths of the E1 carboxy terminus to affinity-purify a polyclonal antiserum against E1, we have been able to define two epitopes within the last 15 amino acid residues of the protein. These epitope-specific antibodies bind to E1 in Golgi and perinuclear membranes as well as to budding viruses; they do not, however, label the plasma membrane or the membranes of post-Golgi vesicles transporting virions to the cell surface.