A dual-specific Glu-tRNA(Gln) and Asp-tRNA(Asn) amidotransferase is involved in decoding glutamine and asparagine codons in Acidithiobacillus ferrooxidans.

The gatC, gatA and gatB genes encoding the three subunits of glutamyl-tRNA(Gln) amidotransferase from Acidithiobacillus ferrooxidans, an acidophilic bacterium used in bioleaching of minerals, have been cloned and expressed in Escherichia coli. As in Bacillus subtilis the three gat genes are organized in an operon-like structure in A. ferrooxidans. The heterologously overexpressed enzyme converts Glu-tRNA(Gln) to Gln-tRNA(Gln) and Asp-tRNA(Asn) to Asn-tRNA(Asn). Biochemical analysis revealed that neither glutaminyl-tRNA synthetase nor asparaginyl-tRNA synthetase is present in A. ferrooxidans, but that glutamyl-tRNA synthetase and aspartyl-tRNA synthetase enzymes are present in the organism. These data suggest that the transamidation pathway is responsible for the formation of Gln-tRNA and Asn-tRNA in A. ferrooxidans.