23 February 2010

Scientists create tiny RNA molecule with big implications

by Kate Melville

An extremely small RNA molecule created by University of Colorado scientists can catalyze a key reaction needed to synthesize proteins, lending more weight to the theory that all life on Earth evolved from primitive forms of RNA. Reporting their findings in the Proceedings of the National Academy of Sciences, the research team note that the RNA enzyme is the smallest ever known to perform a cellular chemical reaction. The discovery is significant as it shows that even an extremely tiny RNA can by itself catalyze a key reaction needed to synthesize proteins.

The new work is based upon earlier research that showed RNA can act as an enzyme, carrying out chemical reactions. While cellular RNA can have thousands of basic structural units (known as nucleotides), lead researcher Professor Michael Yarus chose to focus on a ribozyme - a form of RNA that can catalyze chemical reactions - with only five nucleotides.

The finding adds weight to the "RNA World" hypothesis, which proposes that life on Earth evolved from early forms of RNA. That hypothesis, however, has always been hamstrung by the fact that RNA molecules are hard to make. "This work shows that RNA enzymes could have been far smaller, and therefore far easier to make under primitive conditions, than anyone has expected," explained Yarus.

If very simple RNA molecules such as the product of Yarus' lab could have accelerated chemical reactions in Earth's primordial stew, the chances are much greater that RNA could direct and accelerate biochemical reactions under primitive conditions.

Farther back in time, before the advent of RNA, most biologists believe there was a simpler world of chemical replicators that could only make more of themselves, given the raw materials of the time. "If there exists that kind of mini-catalyst, a 'sister' to the one we describe, the world of the replicators would also jump a long step closer and we could really feel we were closing in on the first things on Earth that could undergo Darwinian evolution," mused Yarus. But that pre-RNA replicator has not yet been found.

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Source: University of Colorado at Boulder