Functional characterization of Bombyx mori nucleopolyhedrovirus late gene transcription and genome replication factors in the non-permissive insect cell line SF-21

Abstract

We compared the abilities of late gene transcription and DNA replication machineries of the baculoviruses Autographa californica nucleopolyhedrovirus (Ac MNPV) and Bombyx mori NPV (BmNPV) in SF-21 cells, an insect-derived cell line permissive for Ac MNPV infection. It has been well established that 19 Ac MNPV late expression factors ( lefs) stimulate substantial levels of late gene promoter activity in SF-21 cells. Thus, we constructed a set of clones containing the BmNPV homologs of the Ac MNPV lefs under control of the constitutive Drosophila heat shock 70 protein promoter and tested their ability to activate an Ac MNPV late promoter–reporter gene cassette in SF-21 cells. We tested the potential of individual or predicted functional groups of BmNPV lefs to successfully replace the corresponding Ac MNPV gene(s) in transient late gene expression assays. We found that most, but not all, BmNPV lefs were able to either fully or partially substitute for the corresponding Ac MNPV homolog in the context of the remaining Ac MNPV lefs with the exception of BmNPV p143, ie-2, and p35. BmNPV p143 was unable to support late gene expression or be imported into the nucleus of cells in the presence of the Ac MNPV or the BmNPV LEF-3, a P143 nuclear shuttling factor. Our results suggest that host-specific factors may affect the function of homologous proteins.