Co-evolution of the archaeal tRNA-dependent amidotransferase GatCAB with tRNAAsn

The important identity elements in tRNAGln and tRNAAsn for bacterial GatCAB and in tRNAGln for archaeal GatDE are the D-loop and the first base pair of the acceptor stem. Here we show that Methanothermobacter thermautotrophicus GatCAB, the archaeal enzyme, is different as it discriminates Asp-tRNAAsp and Asp-tRNAAsn by use of U49, the D-loop and to a lesser extent the variable loop. Since archaea possess the tRNAGln-specific amidotransferase GatDE, the archaeal GatCAB enzyme evolved to recognize different elements in tRNAAsn than those recognized by GatDE or by the bacterial GatCAB enzyme in their tRNA substrates.