Abortive transcription products of vaccinia virus are guanylylated, methylated, and polyadenylylated.

Abortive transcription products were synthesized in vitro by UV-irradiated vaccinia virus particles that were incubated with all four ribonucleoside triphosphates or by unirradiated particles that were incubated in reaction mixtures deficient in CTP or UTP. The RNA sedimented at 4 to 6S in sucrose gradients, suggesting that premature termination had occurred, presumably in one case because the DNA contained UV-induced pyrimidine dimers and in the other case because of ribonucleoside triphosphate was present at limiting concentration for transcription. Nevertheless, the short transcripts were capped, methylated, and polyadenylylated, indicating that neither completion of an RNA chain nor processing from a polycistronic precursor was required for modification of either end of the RNA. In addition, the finding of m7G(5')pppAm and m7G(5')pppGm at the 5' ends of the short RNA molecules implied that transcription was initiated with both ATP and GTP. The presence of the polyadenylic acid tract suggested that a slow-down or cessation of transcription, rather than a specific 3'-terminal sequence, served as a signal for polyadenylylation.