Transcription of the Vaccinia Virus Genome and the Occurrence of Polyriboadenylic Acid Sequences in Messenger RNA

Abstract

Vaccinia is a large DNA virus which replicates exclusively in the cytoplasm of infected animal cells. Since cellular genes are transcribed preponderantly in the nucleus, we set out several years ago to explore the possibility that vaccinia elaborates an independent and different transcription system in the cytoplasm. It was shown soon thereafter (Kates and McAuslan, 1966, 1967) that purified vaccinia viruses contained within them a DNA-dependent RNA polymerase which was used by the virus shortly after infection for the synthesis of messenger RNA (mRNA) coding for “early” viral functions. The existence of a viral RNA polymerase and the ease of clear-cut separation between host and viral transcription due to the cytoplasmic site of viral replication (Becker and Joklik, 1964) makes vaccinia virus an extremely useful system for a study of control of viral gene expression.