Cleavage of nascent reovirus mRNA by localized activation of the 2'-5'-oligoadenylate-dependent endoribonuclease.

Addition of cell extracts prepared from untreated or interferon-treated cells reduced the yield of reovirus RNA synthesized in transcription reactions with purified virions. The reduction observed with the extract of interferon-treated cells was greater than that observed with the extract of untreated cells. The yield of reovirus RNA could be restored to the level obtained without addition of cell extracts by carrying out transcription either in the presence of an inhibitor of 2'-5'-oligoadenylate (2-5A) synthesis, 2'-dATP, or in the presence of the 3'-methyl analog of 5'-monophosphate 2-5A, which inhibits the 2-5A-dependent endoribonuclease. This enzyme was activated in a localized way since neither mRNA added to transcription reactions containing the extract of interferon-treated cells nor rRNA was appreciably degraded, whereas accumulation of reovirus mRNA was drastically inhibited. These findings provide evidence for an antiviral role of the 2-5A synthetase/endoribonuclease system, which preferentially cleaves nascent viral RNA.