Exploring a novel virus-host interaction in a baculovirus-infected insect cell line

Global protein synthesis is shut down at late times post infection (p.i.) in Ld652Y cells derived from gypsy moth infected with baculovirus Autographa californica nucleopolyhedrovirus (AcMNPV) in the presence of apparently normal mRNAs. A single gene, host range factor 1 (hrf-1) was identified from another baculovirus, Lymantria dispar nucleopolyhedrovirus (LdMNPV), that promoted AcMNPV replication in Ld652Y cells. Recombinant AcMNPVs bearing hrf-1 were constructed that replicated in Ld652Y cells. hrf-1 was transcribed as an early gene and encoded a novel protein of 25.7 kDa that did not have any motif that might imply its function.; Experiments were carried out to investigate the possible connections between apoptosis and protein synthesis shut down. The apogtosis suppressor AcMNPV P35 was translated prior to protein synthesis shut down and functioned to prevent apoptosis in AcMNPV-infected Ld652Y cells. HRF-1 could prevent protein synthesis shut down even when cells were undergoing apoptosis but HRF-1 could not functionally substitute for P35. The DNA synthesis inhibitor aphidicolin could block both apoptosis and protein synthesis shut down in Ld652Y cells induced by p35{dollar}sp{lcub}-{rcub}{dollar} AcMNPV but not protein synthesis shut down in wt AcMNPV-infected Ld652Y cells. These data suggested that protein synthesis shut down and apoptosis were separate responses of Ld652Y cells to AcMNPV infection and that P35 was involved in inducing a second pathway that led to protein synthesis shut down.; A cell-free translation system (cytoplasmic lysate) was established from insect cells and a series of in vitro translation assays were carried out to identify the defect in protein synthesis in AcMNPV-infected Ld652Y cells. Lysate derived from AcMNPV-infected Ld652Y cells at late times p.i. did not display in vitro translation ability but its translation ability could be restored by addition of uncharged eukaryotic tRNA. Our data suggested that the defect of protein synthesis in AcMNPV-infected Ld652Y cells lied in the adaptor ability of a single or a small group of tRNA species and that a common mechanism of protein synthesis shut down was shared in AcMNPV-infected Ld652Y and BmN cells.