Phosphorolytic exoribonuclease that plays an important role in tRNA 3'-end maturation; has no activity on a tRNA precursor with a 3'-terminal phosphate group. In vitro is freely reversible, adds nucleotides to the ends of RNA molecules by using nucleoside diphosphates as substrates, but this may not be physiologically important. Probably plays a role in initiation of 16S rRNA degradation (leading to ribosome degradation) during starvation