Messenger RNAs that are not synthesized by RNA polymerase II can be 3 ' end cleaved and polyadenylated

The poly(A) tail of influenza virus mRNAs is synthesized by the viral RNA p olymerase by reiterative copying of a U5-7 sequence near the 5' end of the viral RNA (vRNA) template. We have engineered a vRNA molecule by replacing its viral U-6 poly(A) site with a negative-sense eukaryotic polyadenylation signal. The vRNA was transcribed by the viral RNA polymerase and the trans cription product was processed by the cellular 3' end processing machinery in vivo. According to the current model, 3' end processing of eukaryotic pr e-mRNAs is coupled to cellular RNA polymerase II (pol II) transcription; th us only RNAs synthesized by pol II are believed to be polyadenylated effici ently. Our results show that the cellular polyadenylation machinery is neve rtheless able to recognize and process RNA transcripts that are not synthes ized by pol II, indicating that synthesis by pol II is not an absolute requ irement for 3' end processing in vivo.