UNIDIRECTIONAL COMPLEMENTATION BETWEEN GLYCOPROTEIN-B HOMOLOGS OF PSEUDORABIES VIRUS AND BOVINE HERPESVIRUS-1 IS DETERMINED BY THE CARBOXYTERMINAL PART OF THE MOLECULE

The most highly conserved glycoproteins in herpesviruses, homologues o f glycoprotein B (gB) of herpes simplex virus, have been shown to play essential roles in membrane fusion during penetration and direct cell -to-cell spread of herpes virions. In studies aimed at assessing wheth er sequence conservation is reflected in the conservation of functiona l properties, we previously showed that bovine herpesvirus 1 (BHV-1) g B was able to functionally complement a gB(-) PrV mutant. To analyse i n detail the function of gB in BHV-1, and to be able to test for recip rocal complementation between pseudorabies virus (PrV) and BHV-1 gB, w e isolated a gB(-) BHV-1 mutant on a cell line stably expressing BHV-1 gB. Functional analysis showed that BHV-1 gB was essential for penetr ation as well as for direct cell-to-cell spread of BHV-1, indicating s imilar functions for PrV and BHV-1 gB. However, PrV gB was unable to c omplement plaque formation, i.e. direct cell-to-cell spread, or penetr ation of gB(-) BHV-1 virions despite its incorporation into the virion envelope. Analysis of cell lines expressing chimeric gB molecules com posed of PrV and BHV-1 gB showed that plaque formation of both gB(-) m utants was complemented when the carboxyterminal half of the chimeric gB was derived from BHV-1 gB and the amino-terminal half from PrV gB. In the opposite case, unidirectional complementation occurred. Althoug h the chimeric molecules were generally less efficient in complementin g infectivity of free virions, a similar complementation pattern was o bserved. In summary, our data show a unidirectional pattern of transco mplementation between the gB glycoproteins of PrV and BHV-1. This indi cates that these proteins are functionally related but not identical. The unidirectional transcomplementation pattern was determined by the provenance of the carboxy-terminal half in chimeric gB proteins indica ting that regions which are important for gB function but differ betwe en PrV and BHV-1 reside in this part of gB.