Two archaeal tRNase Z enzymes: similar but different
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The endoribonuclease tRNase Z plays an essential role in tRNA metabolism by removal of the 3′ trailer element of precursor RNAs. To investigate tRNA processing in archaea, we identified and expressed the tRNase Z from Haloferax volcanii, a halophilic archaeon. The recombinant enzyme is a homodimer and efficiently processes precursor tRNAs. Although the protein is active in vivo at 2–4 M KCl, it is inhibited by high KCl concentrations in vitro, whereas 2–3 M (NH4)2SO4 do not inhibit tRNA processing. Analysis of the metal content of the metal depleted tRNase Z revealed that it still contains 0.4 Zn2+ ions per dimer. In addition tRNase Z requires Mn2+ ions for processing activity. We compared the halophilic tRNase Z to the homologous one from Pyrococcus furiosus, a thermophilic archaeon. Although both enzymes have 46% sequence similarity, they differ in their optimal reaction conditions. Both archaeal tRNase Z proteins process mitochondrial pre-tRNAs. Only the thermophilic tRNase Z shows in addition activity toward intron containing pre-tRNAs, 5′ extended precursors, the phosphodiester bis(p-nitrophenyl)phosphate (bpNPP) and the glyoxalase II substrate S-d-lactoylglutathion (SLG).
KeywordsHaloferax volcanii Pyrococcus furiosus tRNase Z tRNA Processing Metallo-β-lactamase
We appreciate very much discussions about salt requirements of the halophilic enzyme with Prof. Dr. Richard Giége and his helpful advice in analysing processing with ammonium sulphate. We are grateful to Dr. Harald Huber and Prof. Dr. Karl. O. Stetter for the gift of P. furiosus cells. We like to thank Elli Bruckbauer and Ingrid Schleyer for expert technical assistance. Work presented here was funded by the VolkswagenStiftung.
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