My professor had given us a lecture on the RNA World Hypothesis. He provided evidence for this hypothesis by citing the in-vitro selection experiments carried out on RNA. The outcome of one (or more) of these experiments resulted in the "creation" of an RNA polymerase ribozyme which totally blew my mind. It was capable of ligating 10-15 nucleotides on RNA oligonucleotides, which is actually really terrible processivity (but its a goddamn RIBOZYME). A paper had recently solved the structure of this ribozyme and my question to the professor was whether there were any similarities between the ribozyme structure and that of an RNA polymerase. He quickly dismissed my question, stating that the ribozyme is unlike anything seen before :( This actually got me thinking, would different macromolecules (in this case RNA and proteins) converge to similar structures over a long period of time (through evolutionary processes) if they were catalyzing the same reaction? I had difficulty finding papers that compared the structures of ribozymes and proteins with similar function.