This study examines viral protein and DNA synthesis in Spodoptera frugiperda multicapsid nuclear polyhedrosis virus (SfMNPV) infections of S. frugiperda and Trichoplusia ni cells. A total of 28 infected cell specific polypeptides (ICSPs) were detected in the productive S.frugiperda cells. Of these, 14 were identified as structural polypeptides. Based on the change in their rate of synthesis during the replication cycle, these ICSPs were grouped into four classes. Only a 97k and a 29k ICSP were detected in SfMNPV infections of T.ni cells. Inhibition of host protein synthesis occurred in productive infections only, beginning at 10h postinfection (p.i.) and reaching maximal levels by 20 h p.i. The rate of viral DNA synthesis in the productive cells was maximal between 8 to 16 h postinfection, and only low levels of viral DNA were synthesized in T.ni cells. The data suggest that the productive SfMNPV/S.frugiperda cell infection has a gene expression program similar but not identical to that of Autographa californica MNPV infections. The SfMNPV/T.ni cell infection is nonpermissive and is restricted at the earliest phase of the viral gene expression program.
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