Preferential activation of the 8-17 deoxyribozyme by Ca2+ ions -: Evidence for the identity of 8-17 with the catalytic domain of the MG5 deoxyribozyme

The 8-17 deoxyribozyme is a small RNA-cleaving DNA molecule of potential therapeutic interest. Here, the cleavage rates of 16 variants of the 8-17 deoxyribozyme were measured in the presence of different divalent metal ions. Despite the fact that 8-17 was originally selected in vitro for activity in the presence of Mg2+ (Santoro, S. W., and Joyce, G. F. (1997) Proc. Natl. Acad. Sci. U.S. A. 94, 4262-4266) nearly all the 8-17 variants exhibited substantially higher (up to 20-fold) reaction rates in Ca2+ as compared with Mg2+, This preference for calcium ions critically depended on the nucleoside residues at two specific positions of the deoxyribozyme core. The Ca2+ specificity of 8-17 is strongly reminiscent of the properties of Mg5, an RNA phosphodiester-cleaving deoxyribozyme previously isolated by Faulhammer and Famulok (Faulhammer, D., and Famulok, M. (1996) Angew. Chem. Int. Ed. Engl. 35, 2837-2841). Indeed, analysis of the Mg5 sequence revealed the presence of a complete 8-17 motif, coincident with the conserved region of Mg5, An 8-17 deoxyribozyme modeled after the Mg5 conserved region displayed catalytic features comparable with those reported for the full-length Mg5 deoxyribozyme.