Involved in mRNA degradation. Catalyzes the phosphorolysis of single-stranded polyribonucleotides processively in the 3'- to 5'-direction. phosphate + RNA(n+1) = a ribonucleoside 5'-diphosphate + RNA(n) Interacts with RNase E (rne). Some of the protein cosediments with polysomes. Essential, it cannot be deleted. Belongs to the polyribonucleotide nucleotidyltransferase family.