Influenza A virus RNA polymerase has the ability to stutter at the polyadenylation site of a viral RNA template during RNA replication

The viral polymerase of influenza vurus, a negative-strand RNA virus, is be lieved to polyadenylate the mRNAs by stuttering at a stretch of five to sev en uridine residues which are located close to the 5' ends of the viral RNA templates. However, a mechanism of polyadenylation based on a template-ind ependent synthesis of the poly(A) tail has not been excluded. In this repor t, we present new evidence showing the inherent ability of the viral polyme rase to stutter at the poly(U) stretch of a viral RNA template during RNA r eplication. Variants which possess 1- to W-nucleotide-long insertions at th e poly(U) stretch have been identified. These results support a stuttering mechanism for the polyadenylation of influenza virus mRNAs.