Catalyzes the NADPH-dependent reduction of 7-cyano-7-deazaguanine (preQ0) to 7-aminomethyl-7-deazaguanine (preQ1), a late step in the queuosine pathway. 7-aminomethyl-7-carbaguanine + 2 NADP(+) = 7-cyano-7-deazaguanine + 3 H(+) + 2 NADPH Does not require a metal cofactor. Activity is strongly inhibited by Cu(2+) and Fe(3+). kcat is 0.66 min(-1) (at pH 7.5 and 30 degrees Celsius). Optimum pH is 7.5. tRNA modification; tRNA-queuosine biosynthesis. Forms an asymmetric tunnel-fold homodecamer of two head-to-head facing pentamers, harboring 10 active sites at the intersubunit interfaces. Belongs to the GTP cyclohydrolase I family. QueF type 1 subfamily. Crystallographic structure revealed that QueF enzyme forms an asymmetric tunnel-fold homodecamer (PubMed:22787148) and not a homododecamer as originally proposed (PubMed:15767583).