Selenocysteine tRNA and serine tRNA are aminoacylated by the same synthetase, but may manifest different identities with respect to the long extra arm.
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.
Ohama
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Laboratory of Experimental Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
Yang
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Hatfield
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D000818:Animals; D000926:Anticodon; D001483:Base Sequence; D003001:Cloning, Molecular; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009690:Nucleic Acid Conformation; D012345:RNA, Transfer, Amino Acid-Specific / Q000378:metabolism; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism*; D011817:Rabbits; D012714:Serine-tRNA Ligase / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D046249:Transfer RNA Aminoacylation
D000926:Anticodon; D012345:RNA, Transfer, Amino Acid-Specific; D012346:RNA, Transfer, Amino Acyl; C036928:tRNA, selenocysteine-; D012714:Serine-tRNA Ligase