Recognition of tRNA His in an RNase P-Free Nanoarchaeum

The 5' extra guanosine with 5'-monophosphate at position -1 (G-1) of tRNA (p-tRNA ) is a nearly universal feature that establishes tRNA identity. G-1 is either genome encoded and retained after processing by RNase P (RNase P) or posttranscriptionally incorporated by tRNA guanylyltransferase (Thg1) after RNase P cleavage. However, RNase P is not found in the hyperthermophilic archaeum Nanoarchaeum equitans; instead, all of its tRNAs, including tRNA , are transcribed as leaderless tRNAs with 5'-triphosphate (ppp-tRNAs). How N. equitans histidyl-tRNA synthetase (NeHisRS) recognizes its cognate tRNA (NetRNA ) is of particular interest. In this paper, we show that G-1 serves as the major identity element of NetRNA , with its anticodon performing a similar role, though to a lesser extent. Moreover, NeHisRS distinctly preferred p-tRNA over ppp-tRNA (~5-fold difference). Unlike other prokaryotic HisRSs, which strongly prefer tRNA with C73, this enzyme could charge tRNAs with A73 and C73 with nearly equal efficiency. As a result, mutation at the C73-recognition amino acid residue Q112 had only a minor effect (