5′-End maturation of tRNA in Aquifex aeolicus

5'-End maturation of tRNA primary transcripts is thought to be ubiquitously catalyzed by ribonuclease P (RNase P), a ribonucleoprotein enzyme in the vast majority of organisms and organelles. In the hyperthermophilic bacterium Aquifex aeolicus, neither a gene for the RNA nor the protein component of bacterial RNase P has been identified in its sequenced genome. Here, we demonstrate the presence of an RNase P-like activity in cell lysates of A. aeolicus. Detection of activity was sensitive to the buffer conditions during cell lysis and partial purification, explaining why we failed to observe activity in the buffer system applied previously. RNase P-like activity of A. aeolicus depends on the presence of Mg2+ or Mn2+, persists at high temperatures, which inactivate RNase P enzymes from mesophilic bacteria, and is remarkably resistant to micrococcal nuclease treatment. While cellular RNA fractions from other Aquificales (A. pyrophilus, Hydrogenobacter thermophilus and Thermocrinis ruber) could be stimulated by bacterial RNase P proteins to catalyze tRNA 5'-end maturation, no such stimulation was observed with RNA from A. aeolicus. In conclusion, our results point to the possibility that RNase P-like activity in A. aeolicus is devoid of an RNA subunit or may include an RNA subunit with untypical features.