The synthesis of α (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 α mRNA was translated either in the presence of actinomycin D to prevent further mRNA synthesis, or . In intact cells three electrophoretically distinct virus-specific proteins were synthesized, with apparent molecular weights of approximately 180000 (A), 190000 (B) and 200000 (C). The accumulation of B and C was prevented by the proline analogue azetidine. Only protein A was detected . Proteins B and C were not detected in normally infected cells. All three 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. It is presumed that 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 it is possible that they represent stages in the formation or transport of A within the cell and that the progression depends on an unstable protein which is depleted in cells treated with cycloheximide.


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