Through the looking glass: A cross-chiral reaction challenges our definition of life

Just like your left and right hand exist as mirror images of each other, many biological molecules have their own form of left- and right-handedness, called chirality. On Earth, all RNA exists in a right-handed chiral form. Even when scientists make synthetic left-handed versions, the two groups behave as if on opposite sides of a mirror, unable to interact with each other. But what if they could? What if a molecule could reach through the mirror and interact with the reflected world on the other side? What if this set off a chain reaction that got molecules on both sides working together in ways we’ve never seen before? Using sophisticated bioengineering techniques, Salk President and Professor Gerald Joyce, senior staff scientist David Horning, and colleagues engineered a chemical system in which left- and right-handed versions of an RNA enzyme could effectively “reach through the mirror” and replicate each other exponentially and indefinitely. This is the first evidence of a life-like chemical system that operates on both sides of the mirror of chirality, creating the opportunity to study an entirely new form of biochemical evolution. The achievement could also advance the development of cross-chiral therapeutics, diagnostics, and other biotechnologies.

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