Transfer RNA-dependent amino acid biosynthesis: An essential route to asparagine formation

^†Departments of Molecular Biophysics and Biochemistry and ^§Chemistry, Yale University, New Haven, CT 06520-8114; and ^‡Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0308

Contributed by Dieter Söll

Abstract

Biochemical experiments and genomic sequence analysis showed that Deinococcus radiodurans and Thermus thermophilus do not possess asparagine synthetase (encoded by asnA or asnB), the enzyme forming asparagine from aspartate. Instead these organisms derive asparagine from asparaginyl-tRNA, which is made from aspartate in the tRNA-dependent transamidation pathway [Becker, H. D. & Kern, D. (1998) Proc. Natl. Acad. Sci. USA 95, 12832–12837; and Curnow, A. W., Tumbula, D. L., Pelaschier, J. T., Min, B. & Söll, D. (1998) Proc. Natl. Acad. Sci. USA 95, 12838–12843]. A genetic knockout disrupting this pathway deprives D. radiodurans of the ability to synthesize asparagine and confers asparagine auxotrophy. The organism's capacity to make asparagine could be restored by transformation with Escherichia coli asnB. This result demonstrates that in Deinococcus, the only route to asparagine is via asparaginyl-tRNA. Analysis of the completed genomes of many bacteria reveal that, barring the existence of an unknown pathway of asparagine biosynthesis, a wide spectrum of bacteria rely on the tRNA-dependent transamidation pathway as the sole route to asparagine.

Footnotes

↵ ¶ To whom reprint requests should be addressed at: Department of Molecular Biophysics and Biochemistry, Yale University, P.O. Box 208114, 266 Whitney Avenue, New Haven, CT 06520-8114. E-mail: soll{at}trna.chem.yale.edu.
Abbreviations:

AspRS,

aspartyl-tRNA synthetase;

Asp-AdT,

Asp-tRNAAsn amidotransferase;

AsnRS,

asparaginyl-tRNA synthetase