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Nat Struct Mol Biol. 2008 May;15(5):507-14. doi: 10.1038/nsmb.1423. Epub 2008 Apr 20.

Aminoacylation of tRNA with phosphoserine for synthesis of cysteinyl-tRNA(Cys).

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Department of Biochemistry and Molecular Biology, 233 South 10th Street, Philadelphia, Pennsylvania 19107, USA.


Cysteinyl-tRNA(Cys) (Cys-tRNA(Cys)) is required for translation and is typically synthesized by cysteinyl-tRNA synthetase (CysRS). However, Methanocaldococcus jannaschii synthesizes Cys-tRNA(Cys) by an indirect pathway, whereby O-phosphoseryl-tRNA synthetase (SepRS) acylates tRNA(Cys) with phosphoserine (Sep), and Sep-tRNA-Cys-tRNA synthase (SepCysS) converts the tRNA-bound phosphoserine to cysteine. We show here that M. jannaschii SepRS differs from CysRS by recruiting the m1G37 modification as a determinant for aminoacylation, and in showing limited discrimination against mutations of conserved nucleotides. Kinetic and binding measurements show that both SepRS and SepCysS bind the reaction intermediate Sep-tRNA(Cys) tightly, and these two enzymes form a stable binary complex that promotes conversion of the intermediate to the product and sequesters the intermediate from binding to elongation factor EF-1alpha or infiltrating into the ribosome. These results highlight the importance of the protein binary complex for efficient synthesis of Cys-tRNA(Cys).

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