Selenocysteine tRNA and serine tRNA are aminoacylated by the same synthetase, but may manifest different identities with respect to the long extra arm.

Abstract

Selenocysteine (Sec) tRNA([Ser])Sec donates Sec to protein, but interestingly, this amino acid is synthesized on tRNA which is first aminoacylated with serine. Thus, the identity elements in tRNA([Ser])Sec for aminoacylation correspond to elements for seryl-tRNA synthetase recognition. As tRNA([Ser])Sec has low homology to the tRNA(Ser) isoacceptors, it would seem then that the identity elements in tRNA([Ser])Sec involve (1) very specific sequences, (2) conformational features, and/or (3) different points or domains for tRNA[Ser]Sec:synthetase and tRNASer:synthetase recognition. Initially, we confirmed that the same synthetase aminoacylates both tRNAs by showing that a mutant tRNA[Ser]Sec which has a blocked 3'-terminus is a competitive inhibitor of tRNASer aminoacylation with a partially purified and a highly purified seryl-tRNA synthetase preparation. The discriminator base (base G73) is essential for aminoacylation of tRNA([Ser])Sec and tRNA(Ser), while the long extra arm plays an important role which seems to be orientation- and length-specific in tRNA(Ser) and, in addition, may manifest sequence specificity in tRNA([Ser])Sec. This difference in the tRNA recognition specificity is discussed. The acceptor stem, DHU stem, and T phi C stem contribute to the recognition process, but to a lesser extent than the discriminator base and the long extra arm.

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@article{Ohama1994SelenocysteineTA, title={Selenocysteine tRNA and serine tRNA are aminoacylated by the same synthetase, but may manifest different identities with respect to the long extra arm.}, author={Takashi Ohama and D C Yang and D. Hatfield}, journal={Archives of biochemistry and biophysics}, year={1994}, volume={315 2}, pages={293-301} }