Exchanges the guanine residue with 7-cyano-7-deazaguanine (preQ0) at position 15 in the dihydrouridine loop (D-loop) of archaeal tRNAs. 7-cyano-7-deazaguanine + guanosine(15) in tRNA = 7-cyano-7-carbaguanosine(15) in tRNA + guanine Binds 1 zinc ion per subunit. tRNA modification; archaeosine-tRNA biosynthesis. Belongs to the archaeosine tRNA-ribosyltransferase family.