Study of a hammerhead ribozyme containing 2'-modified adenosine residues.

The improved synthesis of 2'-fluoro-2'-deoxyadenosine (2'-FA) starting from adenosine is described. This compound was converted to the phosphoramidite and incorporated into a hammerhead ribozyme RNA with the use of automated RNA synthesis techniques. Ribozymes containing 2'-deoxy-adenosine (2'-dA) were prepared in a similar manner. A kinetic rate comparison of the unmodified ribozyme with two ribozymes that had every adenosine replaced with 2'FA or 2'-dA revealed a large decrease in catalytic efficiency (kcat/Km) for the modified ribozymes resulting from a drop in kcat. The kinetic analysis of a number of partially substituted 2'-FA or 2'-dA containing hammerheads revealed that the decrease in activity was not associated with any particular residue but was the result of the accumulation of modified nucleosides within the structure.