Studies ofChoristoneura fumiferanaNuclear Polyhedrosis Virus Gene Expression in Insect Cells

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To investigate the mechanisms regulating baculovirus virulence and host range we have begun to studyChoristoneura fumiferananuclear polyhedrosis virus (CfMNPV) and its gene expression in permissive and nonpermissive cells. We have identified and mapped three genes on the CfMNPV genome. Thepolyhedringene is located from 0.0 to 2.0 m.u. and two other genes,dnapolandp143,both of which are essential for baculovirus DNA replication, are located from 35.3 to 40.9 m.u. and 55.5 to 63.4 m.u., respectively. To gain insight into the expression of CfMNPV genes in permissiveC. fumiferanaand nonpermissiveSpodoptera frugiperdacells, we constructed three expression plasmids in which the promoter region of thednapol,thep143,andpolyhedringenes were placed in front of a chloramphenicol acetyltransferase reporter gene. All three CfMNPV promoters were active in nonpermissive cells in the presence ofAutographa californicanuclear polyhedrosis virus (AcMNPV) DNA, but no activity was detected in permissive cells either in the presence of CfMNPV DNA or AcMNPV DNA. This lack of promoter activity was not due to failure of viral or plasmid DNA to enter the cell nucleus. It was possible that the reporter plasmids were inefficient templates for transcriptional transactivation so we developed a CfMNPV transfer vector and generated a recombinant virus in which thepolyhedrinpromoter driving CAT gene cassette was integrated into the CfMNPV genome. In this case, the CfMNPVpolyhedrinpromoter was highly active in the permissive cells.