Glu-tRNA(Gln) amidotransferase: A novel heterotrimeric enzyme required for correct decoding of glutamine codons during translation

The three genes, gatC, gatA, and gatB, which constitute the transcriptional unit of the Bacillus subtilis glutamyl-tRNA(Gln) amidotransferase have been cloned. Expression of this transcriptional unit results in the production of a heterotrimeric protein that has been purified to homogeneity. The enzyme furnishes a means for formation of correctly charged Gln-tRNA(Gln) through the transamidation of misacylated Glu-tRNA(Gln), functionally replacing the lack of glutaminyl-tRNA synthetase activity in Gram-positive eubacteria, cyanobacteria, Archaea, and organelles. Disruption of this operon is lethal. This demonstrates that transamidation is the only pathway to Gln-tRNA(Gln) in B. subtilis and that glutamyl-tRNA(Gln) amidotransferase is a novel and essential component of the translational apparatus.