Autographa californica M nucleopolyhedrovirus chiA is required for processing of V-CATH

Infection of permissive insect hosts by the baculovirus Autographa californ ica M nucleopolyhedrovirus results in liquefaction, a pathogenic effect tha t enhances the dispersal of progeny virions. Two viral gene products-a prot ease, V-CATH, and a chitinase, chiA-have been shown to be required for liqu efaction to occur. It has been generally accepted that the primary function s of these proteins is to degrade the proteinaceous and chitinous component s of the host cadaver, respectively. We have generated suggestive evidence, however, that chiA may also serve as a molecular chaperone for proV-CATH, the precursor of V-CATH. When cells were infected with virus lacking a func tional chiA gene, proV-CATH failed to undergo processing in vivo and in vit ro and formed insoluble aggregates in the endoplasmic reticulum of infected cells. Thus, expression of chiA may be required for the proper folding of the nascent V-CATH polypeptide in the endoplasmic reticulum. Identical resu lts were obtained when tunicamycin was used to block N-linked glycosylation in cells infected with wildtype virus, suggesting that the putative chiA/V -CATH interaction is mediated by N-linked oligosaccharides. (C) 2000 Academ ic Press.