IUBMB Enzyme Nomenclature


Accepted name: O-phospho-L-serine—tRNA ligase

Reaction: ATP + O-phospho-L-serine + tRNACys = AMP + diphosphate + O-phospho-L-seryl-tRNACys

Other name(s): non-canonical O-phosphoseryl-tRNA synthetase; SepRS; O-phosphoseryl-tRNA ligase

Systematic name: O-phospho-L-serine:tRNACys ligase (AMP-forming)

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 ligates O-phosphoserine to tRNACys, and EC (O-phospho-L-seryl-tRNA: Cys-tRNA synthase) 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 and EC (O-phospho-L-seryl-tRNA: Cys-tRNA synthase) [2].

Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, PDB, CAS registry number:


1. Fukunaga, R. and Yokoyama, S. Structural insights into the first step of RNA-dependent cysteine biosynthesis in archaea. Nat. Struct. Mol. Biol. 14 (2007) 272-279. [PMID: 17351629]

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]

[EC created 2009]

Return to EC 6.1.1 home page
Return to EC 6.1 home page
Return to EC 6 home page
Return to Enzymes home page
Return to IUBMB Biochemical Nomenclature home page