Synthesis of (Immediate-Early) Proteins in Vero Cells Infected with Pseudorabies Virus

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Abstract
The synthesis of .alpha. (immediate-early) polypeptides in Vero cells infected with pseudorabies virus was studied. Cycloheximide was added at the beginning of infection and removed several hours later. The accumulated .alpha. mRNA was translated either in vivo in the presence of actinomycin D to prevent further mRNA synthesis, or in vitro. In intact cells 3 electrophoretically distinct virus-specific proteins were synthesized, with apparent MW of .apprx. 180,000 (A), 190,000 (B) and 200,000 (C). The accumulation of B and C was prevented by the proline analog azetidine. Only protein A was detected in vitro. Proteins B and C were not detected in normally infected cells. All 3 were associated with the nuclear fraction of cell homogenates and A and B were phosphorylated. The radioactivity of B and C declined during a chase period, while that of A increased. This change was prevented by adding cycloheximide during the chase. The pattern of chymotrypsin digestion products suggested that A and B at least were similar proteins. Presumably, protein A is the single immediate-early protein previously described and analogous to ICP 4 of herpes simplex virus. The significance and function, if any, of proteins B and C is not known, but they may represent stages in the formation or transport of A within the cell, the progression depending on an unstable protein which is depleted in cells treated with cycloheximide.