Differential Infectivity of TwoAutographa californicaNucleopolyhedrovirus Mutants on Three Permissive Cell Lines Is the Result oflef-7Deletion

Abstract

We isolated twoAutographa californicanucleopolyhedrovirus (AcMNPV) mutants that have infectivity similar to that of wild-type (wt) AcMNPV in TN368 cells, but reduced budded virus and polyhedral inclusion body production in IPLB-SF-21 and SE1c cells. Restriction endonuclease analysis and sequence analysis indicated that 3.2-kb (77.0–79.4 m.u.) and 4.4-kb (76.7–80.1 m.u.) regions, the location of four major open reading frames (ORFs),pk2,ORF-247,lef-7,and chitinase, were deleted in mutant T295 and T297, respectively. Phenotypes of recombinant viruses vdel-AG, in which all four ORFs were deleted, and vlef7-AG, in which onlylef-7was deleted, were identical to the mutants. The phenotypes of recombinant viruses with deletions of the other ORFs were indistinguishable from wt AcMNPV. This demonstrated that the deletion oflef-7was responsible for the mutant phenotypes. Viral DNA synthesis in both mutant- and vlef7-AG-infected SF-21 and SE1c cells was reduced to less than 10% of that of wt AcMNPV-infected cells. In TN368 cells, DNA synthesis in mutant- and vlef7-AG-infected cells was delayed relative to wt-infected cells. Althoughlef-7is not essential for AcMNPV infection in TN368 cells, it is expressed in TN368, SF-21, and SE1c cells in a similar manner.