Origins of life: RNA made in its own mirror image.

Abstract

An RNA enzyme has been generated that can assemble a mirror-image version of itself. The finding helps to answer a long-standing conundrum about how RNA molecules could have proliferated on prebiotic Earth. See Letter p.440 It is widely assumed that homochirality is a requirement for life and that biological macromolecules must be of the same stereochemical 'handedness' to interact efficiently. Working with Leslie Orgel and others, Gerald Joyce extended this idea in 1984 to suggest that homochirality may also be essential for the origins of life, as templated polymerization of RNA occurs readily in a homochiral system but is impaired in racemic mixtures. Now Joyce and co-author Jonathan Sczepanski show that RNAs of opposing chirality can work together. They devised a D-RNA enzyme that catalyses the polymerization of L-RNA on a L-RNA template — and vice versa. The catalytic potency of this ribozyme is sufficient for it to synthesize its own enantiomer by joining 11 component oligonucleotides. The ribozyme is thought to interact with its substrates via tertiary contacts rather than Watson–Crick base pairing. This unexpected finding will add a new dimension to thoughts on how life could have emerged in an 'RNA world'.