Aminoacyl-tRNA synthesis in Archaea.

The mechanism of aminoacyl-tRNA synthesis differs substantially between Archaea, Bacteria and Eukarya. Sequencing of archaeal genomes has suggested that the asparaginyl-, cysteinyl-, glutaminyl- and lysyl-tRNA synthetases are absent from a number of organisms in this kingdom. The absence of the asparaginyl- and glutaminyl-tRNA synthetases is in agreement with the observation that Asn-tRNA and Gln-tRNA are synthesized by tRNA-dependent transamidation of Asp-tRNA and Glu-tRNA respectively in the archaeon Haloferax volcanii. Biochemical and genetic studies have now shown that while the cysteinyl- and lysyl-tRNA synthetases are present, the enzymes responsible for these activities are unique to Archaea.