IUBMB Enzyme Nomenclature


Accepted name: archaeosine synthase

Reaction: L-glutamine + 7-cyano-7-carbaguanine15 in tRNA + H2O = L-glutamate + archaeine15 in tRNA

Glossary: 7-cyano-7-carbaguanine = preQ0 = 7-cyano-7-deazaguanine
archaeine = 7-deaza-7-carbamidoylguanine = base G*
archaeosine = G* = 7-amidino-7-deazaguanosine

Other name(s): ArcS; TgtA2; MJ1022 (gene name); glutamine:preQ0-tRNA amidinotransferase (incorrect)

Systematic name: L-glutamine:7-cyano-7-carbaguanine aminotransferase

Comments: In Euryarchaeota the reaction is catalysed by ArcS [1,2]. In Crenarchaeota, which do not have an ArcS homologue, the reaction is catalysed either by a homologue of EC, 7-cyano-7-deazaguanine synthase that includes a glutaminase domain (cf. EC, or by a homologue of EC, preQ1 synthase [2]. The enzyme from the Euryarchaeon Methanocaldococcus jannaschii can also use arginine and ammonium as amino donors.

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


1. Phillips, G., Chikwana, V.M., Maxwell, A., El-Yacoubi, B., Swairjo, M.A., Iwata-Reuyl, D. and de Crecy-Lagard, V. Discovery and characterization of an amidinotransferase involved in the modification of archaeal tRNA. J. Biol. Chem. 285 (2010) 12706-12713. [PMID: 20129918]

2. Phillips, G., Swairjo, M.A., Gaston, K.W., Bailly, M., Limbach, P.A., Iwata-Reuyl, D. and de Crecy-Lagard, V. Diversity of archaeosine synthesis in crenarchaeota. ACS Chem. Biol. 7 (2012) 300-305. [PMID: 22032275]

[EC created 2012]

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