IUBMB Enzyme Nomenclature


Accepted name: O-phospho-L-seryl-tRNA:Cys-tRNA synthase

Reaction: O-phospho-L-seryl-tRNACys + sulfide = L-cysteinyl-tRNACys + phosphate

Other name(s): SepCysS; Sep-tRNA:Cys-tRNA synthase

Systematic name: O-phospho-L-seryl-tRNACys:hydrogen sulfide 2-aminopropanoate transferase

Comments: In organisms like Archaeoglobus fulgidus lacking EC (cysteine—tRNA ligase) for the direct Cys-tRNACys formation, Cys-tRNACys is produced by an indirect pathway, in which EC (O-phosphoseryl-tRNA ligase) ligates O-phosphoserine to tRNACys, and EC converts the produced O-phospho-L-seryl-tRNACys to Cys-tRNACys. The SepRS/SepCysS pathway is the sole route for cysteine biosynthesis in the organism [1]. Methanosarcina mazei can use both pathways, the direct route using EC (cysteine—tRNA ligase) and the indirect pathway with EC (O-phosphoseryl-tRNA ligase) and EC [2].

Links to other databases: BRENDA, EXPASY, KEGG, PDB, Metacyc, CAS registry number: 1239229-21-0


1. Fukunaga, R. and Yokoyama, S. Structural insights into the second step of RNA-dependent cysteine biosynthesis in archaea: crystal structure of Sep-tRNA:Cys-tRNA synthase from Archaeoglobus fulgidus. J. Mol. Biol. 370 (2007) 128-141. [PMID: 17512006]

2. Hauenstein, S.I. and Perona, J.J. Redundant synthesis of cysteinyl-tRNACys in Methanosarcina mazei. J. Biol. Chem. 283 (2008) 22007-22017. [PMID: 18559341]

3. Yuan, J., Palioura, S., Salazar, J.C., Su, D., O'Donoghue, P., Hohn, M.J., Cardoso, A.M., Whitman, W.B. and Soll, D. RNA-dependent conversion of phosphoserine forms selenocysteine in eukaryotes and archaea. Proc. Natl. Acad. Sci. USA 103 (2006) 18923-18927. [PMID: 17142313]

[EC created 2009]

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