For decades, many researchers thought that ribonucleic acid, or RNA, was nothing more than a molecular interpreter that helps translate DNA codes into proteins. But research over the past 15 years, including studies at the Whitehead Institute, has been lending credence to the notion of a so-called "RNA world," an era in early evolution when all life forms were based on RNA.
This view faced a difficulty, however. For RNA-based life to survive, it must have acquired the ability to synthesize its own building blocks, and until now, scientists had not found an RNA molecule with this key characteristic.
In this week's issue of Nature, Drs. David Bartel and Peter Unrau of the Whitehead Institute report that they have found an RNA molecule capable of making a nucleotide building block, providing some of the strongest evidence yet to support the RNA world view. In contemporary metabolism, protein enzymes catalyze this nucleotide-synthesis reaction, which involves the addition of a nucleotide base to a sugar phosphate. For the RNA world scenario to be feasible, scientists had to show that RNA molecules could catalyze this reaction without the help of protein enzymes.
The Bartel lab finding provides this evidence and supports the theory that in early evolution, RNA molecules carried out functions now considered to be the domains of DNA and proteins: like DNA in modern biology, RNA stored the genetic information to reproduce, and like protein, RNA synthesized the molecules needed to reproduce.
These and other findings will ultimately help evolutionary biologists address questions about how life began on earth more than three billion years ago.
Theories about the origins of life have long intrigued scientists and lay people alike. "A fundamental question about the origin of life is what class of molecules gave rise to some of the earliest life forms" says Dr. Bartel.