SELF-INCORPORATION OF COENZYMES BY RIBOZYMES

RNA molecules that are assembled from the four standard nucleotides co ntain a limited number of chemical functional groups, a characteristic that is generally thought to restrict the potential for catalysis by ribozymes. Although polypeptides carry a wider range of functional gro ups, many contemporary protein-based enzymes employ coenzymes to augme nt their capabilities. The coenzymes possess additional chemical moiet ies that can participate directly in catalysis and thereby enhance cat alytic function. In this work, we demonstrate a mechanism by which rib ozymes can supplement their limited repertoire of functional groups th rough RNA-catalyzed incorporation of various coenzymes and coenzyme an alogues. The group I ribozyme of Tetrahymena thermophila normally medi ates a phosphoester transfer reaction that results in the covalent att achment of guanosine to the ribozyme. Here, a shortened version of the ribozyme is shown to catalyze the self-incorporation of coenzymes and coenzyme analogues, such as NAD(+) and dephosphorylated CoA-SH. Simil ar ribozyme activities may have played an important role in the ''RNA world,'' when RNA enzymes are thought to have maintained a complex met abolism in the absence of proteins and would have benefited from the i nclusion of additional functional groups.