Functional equivalence of the uridine turn and the hairpin as building blocks of tertiary structure in the Neurospora VS ribozyme

Mutational, kinetic, and chemical modification experiments show that one of the three-way helical junctions in the Neurospora VS ribozyme contains a u ridine turn that is important for organizing the functional three-dimension al structure of this junction. Disruption of the uridine turn disrupts the structure of the junction and decreases the self-cleavage activity of the r ibozyme; however, substitution of the uridine turn with a variety of differ ent hairpins, thereby transforming the three-way junction into a four-way j unction, maintains catalytic activity. Chemical modification structure prob ing reveals that both the native junction and the hairpin-containing juncti on support the same tertiary interactions required elsewhere in the ribozym e for catalysis. These observations show that functionally equivalent three -dimensional RNA structures can be built from different secondary structure elements. (C) 2001 Academic Press.