RNA Offers Clue to Life's Start

Article excerpt

RNA Offers Clue to Life's Start

In answering the question of how life began, biologists can offer only plausible stories. One oft-described scenario highlights ribonucleic acids, or RNA, as the evolutionary link between life's chemical precursors and the first self-replicating cells. In contemporary cells, RNA carries genetic information and plays crucial roles in transforming genetic code into proteins.

To spawn the earliest living cells, RNA would have had to duplicate itself without the complex replicating enzymes and other chemicals used by cells. Researchers have found no such self-replicating molecules in nature.

Now, two molecular biologists claim their laboratory-modified RNA molecules can copy parts of themselves nearly unassisted. The researchers have yet to build an RNA molecule that can copy all of itself, but they say their work renders that goal realistic.

"If we can do this, it would show that self-replicating RNA could have been a major step in the evolution of life," says Jack W. Szostak of Massachusetts General Hospital in Boston. As a first experimental step, he and Jennifer A. Doudna have modified a type of RNA molecule--called a ribozyme -- found in protozoans and some other organisms. Ribozymes' normal role is to extract themselves from larger RNA molecules that contain them.

Other researchers have shown that the protozoan ribozyme can use a short segment on its own molecular body as a template for linking a limited group of short nucleotide sequences, or oligonucleotides. …