Differential infectivity of two Autographa californica nucleopolyhedorvirus mutants on three permissive cell lines is the result of lef-7 deletion

We isolated two Autographa californica nucleopolyhedrovirus (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 only lef-7 was 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 of lef-7 was 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 vlef7AG-infected cells was delayed relative to wt-infected cells. Although lef-7 is not essential for AcMNPV infection in TN368 cells, it is expressed in TN368, SF-21, and SE1c cells in a similar manner.