Catalyzes the base-exchange of a guanine (G) residue with the queuine precursor 7-aminomethyl-7-deazaguanine (PreQ1) at position 34 (anticodon wobble position) in tRNAs with GU(N) anticodons (tRNA-Asp, -Asn, -His and -Tyr). Catalysis occurs through a double-displacement mechanism. The nucleophile active site attacks the C1' of nucleotide 34 to detach the guanine base from the RNA, forming a covalent enzyme-RNA intermediate. The proton acceptor active site deprotonates the incoming PreQ1, allowing a nucleophilic attack on the C1' of the ribose to form the product. After dissociation, two additional enzymatic reactions on the tRNA convert PreQ1 to queuine (Q), resulting in the hypermodified nucleoside queuosine (7-(((4,5-cis-dihydroxy-2-cyclopenten-1-yl)amino)methyl)-7-deazaguanosine). 7-aminomethyl-7-carbaguanine + guanosine(34) in tRNA = 7-aminomethyl-7-carbaguanosine(34) in tRNA + guanine Binds 1 zinc ion per subunit. tRNA modification; tRNA-queuosine biosynthesis. Homodimer. Within each dimer, one monomer is responsible for RNA recognition and catalysis, while the other monomer binds to the replacement base PreQ1. Belongs to the queuine tRNA-ribosyltransferase family.