Baculovirus replication: phosphorylation of polypeptides synthesized in Trichoplusia ni nuclear polyhedrosis virus-infected cells.

A number of polypeptides synthesized specifically in Trichoplusia ni multiple nucleocapsid nuclear polyhedrosis virus (T. ni MNPV)-infected Spodoptera frugiperda cells are phosphorylated both early and late in infection. Certain non-structural proteins and the major basic internal protein are the main phosphoproteins detected in infected cells. The polyhedron protein was not phosphorylated. Many cell proteins continue to be phosphorylated throughout infection. Pulse-chase experiments have shown that some polypeptides are stably phosphorylated whereas other polypeptides (including the major basic protein) have phosphates which cycle on and off. One polypeptide was substantially labelled only after a chase with unlabelled orthophosphate. Fractionation of cells into nucleus and cytoplasm showed that polypeptides located in both the cytoplasm and nucleus were phosphorylated.