EXPRESSION, ASSEMBLY, AND PROTEOLYTIC PROCESSING OF HELMINTHOSPORIUM-VICTORIAE 190S TOTIVIRUS CAPSID PROTEIN IN INSECT CELLS

The dsRNA genome (5.2 kbp) of Helminthosporium victoriae 190S totiviru s (Hv190SV) consists of two large overlapping open reading frames (ORF s). The 5' proximal ORF codes for the capsid protein (CP) and the 3' O RF codes for an RNA-dependent RNA polymerase. Although the capsid of H v190SV is encoded by a single gene, it Is composed of two major closel y related polypeptides, either pas and p83 or pas and p78. Whereas p88 and pas are phosphoproteins, p78 is nonphosphorylated. Expression of the CP ORF in insect cells generated both p78 and pas which assembled into virus-like particles. The finding that p78, p83, and p88 share a common N-terminal amino acid sequence is consistent with the determina tion that N-terminal, but not C-terminal, CP deletions were incompeten t for assembly. Evidence was obtained that p78 is derived from p88 via proteolytic cleavage at the C-terminus. Proteolytic processing may pl ay a regulatory role in the virus life cycle since it leads to dephosp horylation of CP and a subsequent decrease in virion transcriptional a ctivity. (C) 1997 Academic Press.