Infection of Spodoptera frugiperda cells with Autographa californica nuclear polyhedrosis virus I. Synthesis of intracellular proteins after virus infection.

The replication of Autographa californica nuclear polyhedrosis virus (AcNPV) in Spodoptera frugiperda cells in culture has been studied with different methods. The first virus-induced polypeptides (with molecular weights of 46K, 30K, 29K) in infected cells appeared at 3 hr postinfection. Viral DNA synthesis started at about 5 hr postinfection. By electron microscopy, intranuclear nucleocapsids were detected at 10 hr postinfection and at about the same time, the titer of intracellular infectious particles began to rise. The pattern of viral protein synthesis was rather complex; within the first 24 hr postinfection, some 30-35 different polypeptides appeared sequentially in infected cells. Some of these polypeptides seemed to be structural proteins of the virion. The 28K polyhedrin polypeptide was synthesized originally as a precursor and was modified posttranscriptionally. Polyhedrin was synthesized until late in infection. Two distinct stages exist in AcNPV replication: (i) the rapid synthesis of AcNPV-specific nucleic acids and proteins and the assembly of nucleocapsids, some of which develop by budding to extracellular virus; (ii) intranuclear membrane synthesis, polyhedra formation, and occlusion of intranuclear, enveloped virions.