NMR spectroscopic investigations of phosphorothioate containing RNAS

Chirally pure proR(p) phosphorothioates have been introduced 5' to each ade nine residue in the conserved core of the RNA binding site for ribosomal pr otein S8. These backbone modifications prevent Mg2+ coordination and assemb ly of secondary and tertiary structure elements in the core. Cd2+ was found to restore most of the spectral properties characteristic of the native Mg 2+-bound RNA binding site presumably through coordination to one or more ph osphorothioate groups.