Characteristics of an RNA Diels-Alderase active site

The active site components and substrate specificity of an RNA Diels-Aldera se (DA22) were investigated. Diels-Alderase activity was found to be highly dependent on a unique 5-position pyridyl modified uridine. Even closely re lated pyridyl modifications failed to yield active catalysts. Substrate spe cificity of this Diels-Alderase was remarkable. Experiments with alternativ e diene and dienophile substrates showed the active site of the Diels-Alder ase to be highly discriminating, even against molecules of similar reactivi ty and structure. Inhibition studies with a series of product analogues est ablished that the RNA recognizes functional components in and around the re action center of both the diene and the dienophile. Taken together, these r esults suggest that DA22 can fold into a structure that produces an intrica te metal/ligand dependent active site capable of highly specific molecular recognition.