THE CLASS-II MEMBRANE GLYCOPROTEIN-G OF BOVINE RESPIRATORY SYNCYTIAL VIRUS, EXPRESSED FROM A SYNTHETIC OPEN READING FRAME, IS INCORPORATED INTO VIRIONS OF RECOMBINANT BOVINE HERPESVIRUS-1

The bovine herpesvirus 1 (BHV-1) recombinants BHV-1/eG(ori) and BHV-1/ eG(syn) were isolated after insertion of expression cassettes which co ntained either a genomic RNA-derived cDNA fragment (BHV-1/eG(ori)) or a modified, chemically synthesized open reading frame (ORF) (BHV-1/eG( syn)), which both encode the attachment glycoprotein G of bovine respi ratory syncytial virus (BRSV), a class II membrane glycoprotein. North ern blot analyses and nuclear runoff transcription experiments indicat ed that transcripts encompassing the authentic BRSV G ORF were unstabl e in the nucleus of BHV-1/eG(ori)-infected cells. In contrast, high le vels of BRSV G RNA were detected in BHV-1/eG(syn)-infected cells. Immu noblots showed that the BHV-1/eG(syn)-expressed BRSV G glycoprotein co ntains N and O-linked carbohydrates and that it is incorporated into t he membrane of infected cells and into the envelope of BHV-1/eG(syn) v irions. The latter was also demonstrated by neutralization of BHV-1/eG (syn) infectivity by monoclonal antibodies or polyclonal anti-BRSV G a ntisera and complement. Our results show that expression of the BRSV G glycoprotein by BHV-1 was dependent on the modification of the BRSV G ORF and indicate that incorporation of class II membrane glycoprotein s into BHV-1 virions does not necessarily require BHV-1-specific signa ls. This raises the possibility of targeting heterologous polypeptides to the viral envelope, which might enable the construction of BHV-1 r ecombinants with new biological properties and the development of impr oved BHV-1-based live and inactivated vector vaccines.