SANTA CRUZ, CA -- Researchers at the University of California, Santa Cruz, have determined the three-dimensional structure of an RNA enzyme, or "ribozyme," that carries out a fundamental reaction required to make new RNA molecules. Their results provide insight into what may have been the first self-replicating molecule to arise billions of years ago on the evolutionary path toward the emergence of life.
In all forms of life known today, the synthesis of DNA and RNA molecules is carried out by enzymes made of proteins. The instructions for making those proteins are contained in genes made of DNA or RNA (nucleic acids). The circularity of this process poses a challenge for theories about the origins of life.
"Which came first, nucleic acids or proteins? This question once seemed an intractable paradox, but with the discovery of ribozymes, it is now possible to imagine a prebiotic 'RNA World' in which self-replicating ribozymes accomplished both tasks," said William Scott, associate professor of chemistry and biochemistry at UC Santa Cruz.
Scott and postdoctoral researcher Michael Robertson determined the structure of a ribozyme that joins two RNA subunits together in the same reaction that is carried out in biological systems by the protein known as RNA polymerase. Their findings are published in the March 16 issue of the journal Science.
"An RNA-dependent RNA polymerase ribozyme is the foundation of the entire RNA World hypothesis," Robertson said. "With that, you would have an RNA capable of making copies of itself; mutations or errors in some copies would result in variations that would be acted on by Darwinian natural selection, and the molecules would evolve into bigger and better ribozymes. That's what makes this structure so interesting."
Robertson and Scott determined the structure of a ribozyme that is not an entirely self-replicating RNA molecule, but it does carry out the fundamental reaction required
Contact: Tim Stephens
University of California - Santa Cruz