A protein subunit of human RNase P, Rpp14, and its interacting partner, OIP2, have 3′→5′ exoribonuclease activity

The processing of precursor tRNAs at their 5' and 3' termini is a fundamental event in the biosynthesis of tRNA. RNase P is generally responsible for endonucleolytic removal of a leader sequence of precursor tRNA to generate the mature 5' terminus. However, much less is known about the RNase P counterparts or other proteins that are active at the tRNA 3' terminus. Here we show that one of the human RNase P subunits, Rpp14, together with one of its interacting protein partners, OIP2, is a 3'-->5' exoribonuclease with a phosphorolytic activity that processes the 3' terminus of precursor tRNA. Immunoprecipitates of a crude human RNase P complex can process both ends of precursor tRNA by hydrolysis, but purified RNase P has no exonuclease activity. Rpp14 and OIP2 may be part of an exosome activity.