Archaeosine synthase (EC 2.6.1.97, ArcS, TgtA2, MJ1022 (gene), glutamine:preQ0-tRNA amidinotransferase) is an enzyme with systematic name L-glutamine:7-cyano-7-carbaguanine aminotransferase.
[1][2] This enzyme catalyses the following chemical reaction In Euryarchaeota the reaction is catalysed by ArcS.