Δ2-Isopentenylpyrophosphate: Transfer Ribonucleic Acid Δ2-Isopentenyltransferase from Escherichia coli

Δ2-Isopentenylpyrophosphate:tRNA Δ2-isopentenyltransferase, which catalyzes the synthesis of N6-(Δ2-isopentenyl) adenosine in tRNA, has been purified 550-fold from cell-free extracts of Escherichia coli. The enzyme requires tRNA, Δ3-isopentenylpyrophosphate, isopentenylpyrophosphate isomerase, Mg2+, and 2-mercaptoethanol for activity. The enzyme will react only with a suitable tRNA substrate, i.e. one lacking the isopentenyl modification normally present in vivo. The tRNA modified in vitro contains N6-(Δ2-isopentenyl)adenosine adjacent to the 3′ end of the anticodon in the sequence AAAΨ, the sequence normally modified in vivo.