Polyadenylation of viral mRNA through a polymerase stuttering mechanism. The stop signal present at the end of each gene comprises a stretch of uridine on which the viral polymerase acquires a stuttering behavior: after each adenine inserted, the polymerase moves back one nucleotide along with the mRNA. It resumes transcription adding a new adenine, then again moves back, thereby producing a polyA tail.
polyA stuttering