Presence of poly(A) and poly(A)-rich tails in a positive-strand RNA virus known to lack 3׳ poly(A) tails.

Here we show that Tobacco mosaic virus (TMV), a positive-strand RNA virus known to end with 3׳ tRNA-like structures, does possess a small fraction of gRNA bearing polyadenylate tails. Particularly, many tails are at sites corresponding to the 3׳ end of near full length gRNA, and are composed of poly(A)-rich sequences containing the other nucleotides in addition to adenosine, resembling the degradation-stimulating poly(A) tails observed in all biological kingdoms. Further investigations demonstrate that these polyadenylated RNA species are not enriched in chloroplasts. Silencing of cpPNPase, a chloroplast-localized polynucleotide polymerase known to not only polymerize the poly(A)-rich tails but act as a 3׳ to 5׳ exoribonuclease, does not change the profile of polyadenylate tails associated with TMV RNA. Nevertheless, because similar tails were also detected in other phylogenetically distinct positive-strand RNA viruses lacking poly(A) tails, such kind of polyadenylation may reflect a common but as-yet-unknown interface between hosts and viruses.