RNA Diels-Alderases: Relationships between unique sequences and catalytic function

A group of eight unique RNA sequences isolated from a single in vitro selec tion experiment were characterized based on their Diels-Alderase properties ; Five of the eight isolates contain a 10-base conserved region, while the remaining three do not share any sequence similarities with any of the othe rs. This series of RNA Diels-Alderases displayed k(cat), and K-m values tha t spanned 74 and 80-fold ranges, respectively. These values appeared to com pensate for one another, as the value of k(cat)/K-m varied by only 5-fold a mong the isolates studied. Product inhibition experiments revealed a genera l trend between affinity for the cycloaddition product and catalytic abilit y as measured by k(cat),,t. The activities of each of the RNA Diels-Alderas es were completely dependent on the presence of cupric ion. In addition, al l of the RNA catalysts demonstrated a high degree of substrate selectivity, even for structurally and electronically similar dienophiles. Overall, the data demonstrate how a variety of RNA sequences can solve a specific chemi cal problem. The information gathered provides a foundation from which to b uild our understanding of how sequence, structure, and function are interre lated. Such knowledge could be applied to create new catalysts, both large and small.