VP5 OF INFECTIOUS BURSAL DISEASE VIRUS IS NOT ESSENTIAL FOR VIRAL REPLICATION IN CELL-CULTURE

Infectious bursal disease virus (IBDV), a member of the Birnaviridae f amily, encodes in its bisegmented double-stranded RNA genome four stru ctural virion proteins, VP1, VP2, VP3, and VP4, as well as a nonstruct ural protein, VP5, Recently, the establishment of an infectious cRNA s ystem for IBDV has been described (E, Mundt and V. N. Vakharia, Proc, Natl, Acad, Sci, USA 93:11131-11136, 1996), Here, we report the isolat ion of a VP5(-) IBDV mutant constructed by site-directed mutagenesis o f the methionine start codon of VP5, followed by cRNA transfection. Th e resulting virus mutant was replication competent in cell culture, wh ich indicates that VPS is not required for productive replication of I BDV, Absence of VP5 expression was verified by lack of reactivity with newly established anti-Wi monoclonal antibodies and polyclonal sera. VP5(-) IBDV exhibited a delay in replication in chicken embryo cells c ompared to the VP5(+) parental virus, However, final yields were simil ar, Our results thus show that VP5 is nonessential for IBDV replicatio n, which makes it a prime candidate for the construction of deleted, m arked vaccines.