Host-specific transcription of baculovirus genes

We examined the differential replication of Autographa californica multicapsid nuclear polyhedrosis virus (AcMNPV; Family: Baculoviridae) in Spodoptera frugiperda (SF) and Bombyx mori (BM) cell lines. Our previous studies have shown that infection of BM cells is abortive; infectious progeny is not produced, and although virogenic stroma is produced, complete virions or inclusion bodies are not assembled. We designed the present study to determine the extent of infected-cell-specific polypeptides (ICSPs) and viral DNA synthesis in the abortive infection and to see if restriction of virus replication in BM cells is due to a block at the transcriptional level. Pulse-labeling studies showed that a majority of the ICSPs detected in productive SF cells were not synthesized in BM cells. Many of these ICSPs were virion components. Viral DNA replicated in BM cells but more slowly and at a much lower level than in SF cells. Northern blot analysis showed that i) AcMNPV immediate-early gene (IE-1) was transcribed in BM cells at higher levels than in SF cells; ii) a delayed-early gene (dnapol) and a late gene (cap) were transcribed at much lower levels in the abortive infection; and iii) a very late gene (polh) was transcribed at extremely low levels in BM cells. We conclude that virus replication in BM cells is primarily restricted during or prior to the delayed-early stage and occurs at the transcriptional level. It appears that the late and very late effects observed are consequences of the primary block.