Involved in the 3'-end maturation of mitochondrial mRNAs, rRNAs and tRNAs. Functions as a poly(A) mRNA 3'-5' degrading phosphorylase and is required for the degradation of highly expressed transcripts of non-coding regions. phosphate + RNA(n+1) = a ribonucleoside 5'-diphosphate + RNA(n) Plants silencing PNP2 stop growing after two to three weeks. Belongs to the polyribonucleotide nucleotidyltransferase family.