Involved in specific tRNA modification. Catalyzes the oxygen-dependent hydroxylation of 2-methylthio-N-6-isopentenyl adenosine (ms2i6A) to produce 2-methylthio-N-6-(cis-hydroxy)isopentenyl adenosine (ms2io6A) at position 37 in tRNAs. 2-methylsulfanyl-N(6)-dimethylallyladenosine(37) in tRNA + AH2 + O2 = A + H2O + N(6)-[(2E)-4-hydroxy-3-methylbut-2-en-1-yl]-2-(methylsulfanyl)adenosine(37) in tRNA Contains a nonheme dinuclear iron cluster. tRNA modification; 2-methylthio-N-6-(cis-hydroxy)isopentenyl adenosine-tRNA biosynthesis. Homodimer. Belongs to the MiaE family.