A single amidotransferase forms asparaginyl-tRNA and glutaminyl-tRNA in Chlamydia trachomatis

Aminoacyl-tRNA is generally formed by aminoacyl-tRNA synthetases, a family of 20 enzymes essential for accurate protein synthesis. However, most bacte ria generate one of the two amide aminoacyl-tRNAs, Asn-tRNA or Gln-tRNA, by transamidation of mischarged AsptRNA(Asn) or Glu-tRNA(Gln) catalyzed by a heterotrimeric amidotransferase (encoded by the gatA, gatB, and gatC genes) . The Chlamydia trachomatis genome sequence reveals genes for 18 synthetase s, whereas those for asparaginyl-tRNA synthetase and glutaminyl-tRNA synthe tase are absent. Yet the genome harbors three gat genes in an operon-like a rrangement (gatCAB). We reasoned that Chlamydia uses the gatCAB-encoded ami dotransferase to generate both Asn-tRNA and Gln-tRNA. C. trachomatis aspart yl-tRNA synthetase and glutamyl-tRNA synthetase were shown to be non-discri minating synthetases that form the misacylated tRNA(Asn) and tRNA(Gln) spec ies. A preparation of pure heterotrimeric recombinant C. trachomatis amidot ransferase converted Asp-tRNA(Asn) and Glu-tRNA(Gln) into Asn-tRNA and Gln- tRNA, respectively. The enzyme used glutamine, asparagine, or ammonia as am ide donors in the presence of either ATP or GTP. These results suggest that C. trachomatis employs the dual specificity gatCAB-encoded amidotransferas e and 18 aminoacyl-tRNA synthetases to create the complete set of 20 aminoa cyl-tRNAs.