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By Root 1230 0

these sensors, though. Instead, he took advantage of the creative powers of evolution. He dumped an assortment of RNA molecules into a flask and then added a particular chemical he wanted his sensor to detect. A few of the RNA molecules bonded clumsily to the chemical while the rest ignored it. Breaker fished out those few good RNA molecules and made new copies of them. He made them sloppily, so that he randomly introduced a few changes to their sequences. In other words, the RNA mutated. When Breaker exposed the mutated RNA molecules to the same chemical again, some of them did an even better job of binding to it. Breaker repeated this cycle of mutation and selection for many rounds, until the RNA molecules could swiftly seize the chemical.

Eventually Breaker and his colleagues were making RNA molecules that could not only grab the chemical but change their shape. These RNA molecules could act like an enzyme, able to cut other RNA molecules in half. Breaker had created an RNA molecule that could sense something in its environment and use the information to do something to other RNA molecules. He dubbed it a riboswitch.

In the years that followed, Breaker created a library of riboswitches. Some can respond precisely to cobalt, others to antibiotics, others to ultraviolet light. RNA’s ability to evolve such a range of riboswitches brought more weight to the RNA-world theory. Breaker then had a thought. If the RNA-world theory was right, then RNA-based life had shifted many of the jobs once carried out by RNA to DNA and proteins. But perhaps RNA had not surrendered all those jobs. Perhaps riboswitches still survive in DNA-based organisms. In some cases, an RNA-based sensor might be superior to one made of protein. Riboswitches are easier to make, Breaker noted, since all a cell needs to do is read a gene and make an RNA copy.

Breaker and his students set out on a search for natural riboswitches. In a few months they had found one in E. coli, which uses this particular riboswitch to sense vitamin B12. E. coli makes its own vitamin B12, which it needs to survive. But above a certain concentration extra B12 is just a waste. E. coli’s riboswitch, Breaker found, binds vitamin B12. The binding causes it to bend into a shape in which it can shut down the protein that makes the vitamin. Breaker couldn’t have fashioned a more elegant riboswitch himself.

Breaker went on to find more riboswitches in E. coli, and then he found more in other species. Most of them keep levels of chemicals in balance by swiftly shutting down genes. Since Breaker discovered riboswitches, other scientists have found RNA doing many other things in E. coli. Some shut genes off, and others switch them on. Some prevent RNA from being turned into proteins, while others keep its iron in balance. Some RNA molecules allow E. coli to communicate with other microbes, and others help it withstand starvation. These RNA molecules form a hidden control network that’s only now emerging from the shadows. Their discovery has helped make the RNA world even more persuasive.

Still, the question of exactly how RNA-based life emerged and then gave rise to DNA-based life gives scientists a lot to argue about. Some believe that RNA could have emerged directly from a lifeless Earth. Its ribose backbone, for example, might have been able to form in desert lakes, where borate can keep the fragile sugar stable for decades. Some argue that other replicating molecules came first and that the RNA world was merely one phase of history.

Like any living thing, RNA life needed some kind of boundary. Some scientists argue that RNA organisms did not make their own membranes but, rather, existed in tiny pores of ocean rocks. As RNA molecules replicated, the new copies spread from chamber to chamber. Other scientists see RNA life packaged in more familiar cells. They are trying to create these organisms from scratch, crafting oily bubbles that can trap RNA molecules. Proof by invention is their strategy.

There’s probably little to fear from the creation of RNA-based life. Most experts suspect