Involved in mRNA degradation. Catalyzes the phosphorolysis of single-stranded polyribonucleotides processively in the 3'- to 5'-direction. Is a global regulator of virulence and persistency. phosphate + RNA(n+1) = a ribonucleoside 5'-diphosphate + RNA(n) Component of the RNA degradosome, which is a multiprotein complex involved in RNA processing and mRNA degradation. Belongs to the polyribonucleotide nucleotidyltransferase family.