Inhibition of the vaccinia virus associated ribonuclease by HeLa S3 cytosol

A ribonuclease associated with purified vaccinia virus is able to degrade into 3S fragments the viral 8–12S mRNAs synthesized $\text{in}\text{vitro}$. This RNase not detected on purified viral cores was shown to be located on the outer side of the viral envelope. When added to reaction mixture, a partially purified HeLa S₃ cytosol fully inhibits the vaccinia virus associated RNase. Other cytosols from very common mammalian cell lines also contain RNase inhibitor and are of interest in order to prepare large amounts of undegraded vaccinia virus mRNAs.