Synthesizes oQ from preQ1 in a single S-adenosylmethionine-requiring step. The ribosyl moiety of AdoMet is transferred and isomerized to the epoxycyclopentane residue of oQ (By similarity). 7-aminomethyl-7-carbaguanosine(34) in tRNA + S-adenosyl-L-methionine = adenine + epoxyqueuosine(34) in tRNA + H(+) + L-methionine tRNA modification; tRNA-queuosine biosynthesis. Belongs to the QueA family.