Cambridge scientists find RNA that copies itself

Scientists in Cambridge have discovered a tiny molecule of RNA that can make copies of itself, in a finding that could help explain how life began on Earth.

The research, led by the Medical Research Council Laboratory of Molecular Biology, was published in the journal Science on 12 February.

The RNA world

All living things today use DNA to store genetic information and proteins to carry out chemical reactions. But each depends on the other, raising the question of how life could have started.

Many scientists believe that early life relied on RNA, a molecule similar to DNA that can both store information and speed up chemical reactions. This idea is known as the RNA world hypothesis.

For it to work, there must have been an RNA molecule able to copy itself. Scientists have created RNA enzymes, known as ribozymes, that can copy other RNA, but they have been large and complex, making it hard to imagine how they could have arisen by chance.

A small discovery

The new ribozyme, called QT45, is just 45 building blocks long. It can make both a complementary strand and a copy of itself, using short three-letter pieces of RNA as raw material.

The reactions took place in slightly alkaline, partly frozen conditions, which the scientists say could have existed on the early Earth. Copying was slow, taking weeks, and the amounts produced were small, but the process was accurate.

Why it matters

Because QT45 is so small, the discovery suggests that RNA molecules able to copy themselves may be much more common than scientists thought. That makes it more plausible that such a molecule could have emerged naturally, without any help.

The researchers say the work bridges an important gap between chemistry and biology.

Cambridge's tradition

The Laboratory of Molecular Biology has a long record of major discoveries, and its scientists have won a dozen Nobel Prizes. Francis Crick and James Watson worked out the structure of DNA in Cambridge in 1953.

What next?

The next challenge for the field is to find RNA that can copy itself efficiently over many generations, a key step towards a system that could evolve.

Scientists say there is still a long way to go to understand how life began, but that the discovery is an important piece of the puzzle.