Is responsible for the final step in the biosynthesis of archaeosine, a modified nucleoside present in the dihydrouridine loop (D-loop) of archaeal tRNA. Catalyzes the conversion of 7-cyano-7-deazaguanine (preQ0)-modified tRNA to archaeosine-tRNA, transforming a nitrile group to a formamidine group. Can use either glutamine, asparagine or ammonium as amino donor. 7-cyano-7-carbaguanosine(15) in tRNA + H2O + L-glutamine = archaeosine(15) in tRNA + L-glutamate Optimum temperature is around 40 degrees Celsius. Activity decreases significantly at temperatures above 45 degrees Celsius. tRNA modification; archaeosine-tRNA biosynthesis. Homodimer. Belongs to the archaeosine synthase type 1 family.