The Colburn strain of simian cytomegalovirus gives high-yield productive infections in both human fibroblasts and Vero cells and in these cells a major "immediate-early" protein of 94K (IE94) has been identified in cycloheximide "reversal" experiments. We demonstrate here that in BALB/c-3T3 or Rat-1 cells infection with CMV (Colburn) does not yield infectious progeny virions or produce cytopathic effects and that the virus fails to replicate its DNA. However, a single, viral-specific phosphorylated protein of molecular weight 94K was overproduced in the nonproductive infections. No other detectable viral polypeptides were synthesized even at late times. Antiserum elicited against this 94K protein in infected BALB/c-3T3 cells immunoprecipitated the IE94 protein from infected HF cells, demonstrating that the same "immediate-early" gene product is expressed in both permissive and nonpermissive cells. Available evidence indicates that the amplified expression of this "immediate-early" gene in rodent cells can be explained by increased reutilization of stabilized 94K specific mRNA as opposed to increased transcription.
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