Synthesis and NMR study of ribo-oligonucleotides forming a hammerhead-type RNA enzyme system

We designed a hammerhead-type ribozyme system which consists of three RNA fragments and synthesized the component and related ribo-oligonucleotides by the solid-phase phosphoramidite method using o-nitrobenzyl groups for 2'-hydroxyl protection. Improved conditions for photolytic removal of the o-nitrobenzyl groups are described. Imino proton NMR spectra of the ribozyme complex were measured. The resonances for the hydrogen-bonded imino protons were assigned by comparison with the spectra of model complexes which contain the base sequences of one or two of the stem regions. The results suggest that the complex indeed forms a hammerhead structure and the loop regions take an ordered conformation in the absence of magnesium ions.