Replies

Reza Ghadiri of the Scripps Research Institute in La Jolla, California, announced the discovery at last week's American Chemical Society meeting in San Francisco. His team found that molecular ecosystems, consisting of a few proteins, could self-replicate, correct replication errors and form complex interactions that are signatures of living systems. "We were surprised that such simple proteins can act as if they had a mind of their own," says Ghadiri.

For decades, many biologists have marked life's beginning as the spontaneous emergence of the first self-replicating molecule on Earth. But identifying that molecule seemed impossible because in modern cells the blueprint for life rests equally on three types of molecules. The nucleic acid DNA stores genetic information, which is then copied into RNA and used to make proteins. Proteins, in turn, act as catalysts necessary for gene replication.

In the 1980s, when researchers discovered that RNA could also catalyse reactions, RNA was hailed as the likely founding molecule. But last summer, Ghadiri showed that it was too early to rule out proteins. They constructed a protein that could act as a blueprint for its own replication. The replicator was a 32-amino-acid peptide that formed the scaffold on which two smaller pieces docked and fused to create an identical 32-amino-acid peptide. The "twins" fell apart, and the cycle repeated (New Scientist, Science, 10 August 1996, p 16).

Self-replicating peptide from the Ghadiri group Severin K, Lee DH, Kennan AJ, and Ghadiri MR, A synthetic peptide ligase. Nature, 389: 706-9, 1997
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Doudna JA, Couture S, and Szostak JW, A multisubunit ribozyme that is a catalyst of and template for complementary strand RNA synthesis. Science, 251: 1605-8, 1991
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Katchalsky's group (Israel) first succeeded in forming polypeptides with Montmorillonite (a highly common clay) up to an efficiency of nearly one hundred percent.
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Chemical replicating patterns
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But Purdue University scientist Jean Chmielewski has developed a system made up of four peptides -- the building blocks for proteins -- that can replicate itself and is capable of adapting to changes in the environment. The findings, published in the Dec. 3 issue of the scientific journal Nature, expand the scientific view of how life began.

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