Differential requirements for baculovirus late expression factor genes in two cell lines.
A plasmid library of 18 late expression factor (LEF) genes (LEF library) from the baculovirus Autographa californica nuclear polyhedrosis virus (AcMNPV) supports transient expression from a late viral promoter in the SF-21 cell line, derived from Spodoptera frugiperda. We found, however, that this LEF library was unable to support expression from the same promoter in the TN-368 cell line, derived from Trichoplusia ni, which is also permissive for AcMNPV replication. To identify the additional factor(s) required for expression in TN-368 cells, we cotransfected the LEF library with clones representing portions of the AcMNPV genome not represented in the LEF library. A single additional gene was identified; this gene corresponded to ORF70 of the complete AcMNPV sequence and potentially encodes a 34-kDa cysteine-rich polypeptide. Because of its differential effect on late gene expression in the two cell lines, we renamed ORF70 hcf-1 (for host cell-specific factor 1). hcf-1 was involved in expression from reporter plasmids under late and very late but not early promoter control, indicating that it was also a LEF gene. Plasmid DNA replication assays indicated that HCF-1 was involved in virus origin-specific DNA replication in TN-368 cells. Three LEF genes, ie-2, lef-7, and p35, required for optimal virus origin-specific plasmid DNA replication or stability in SF-21 cells had little or no influence in TN-368 cells. Thus, as determined by transient-expression assays, cell line-specific and potentially host-specific factors are required for origin-specific DNA replication or stability.
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Department of Entomology, University of Georgia, Athens 30602-2603, USA.
Miller
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D000818:Animals; D002460:Cell Line; D004261:DNA Replication; D015870:Gene Expression; D005814:Genes, Viral; D007313:Insecta; D017924:Nucleopolyhedroviruses / Q000235:genetics* / Q000502:physiology; D016366:Open Reading Frames; D010957:Plasmids; D011401:Promoter Regions, Genetic; D015183:Restriction Mapping; D018411:Spodoptera; D014162:Transfection; D014779:Virus Replication