DNA had one rule. Bacteria didn't get the memo
Every cell in every organism on Earth copies DNA the same way. Except one bacterial protein — quietly doing something scientists had never seen before
Every cell in every organism on Earth copies DNA the same way. Except one bacterial protein — quietly doing something scientists had never seen before. Your DNA has never been created from scratch. Think of it like a recipe — passed down from parent to child over countless generations, all the way back 4 billion years to the earliest life on Earth. With tweaks and changes accumulating along the way, but always copied from something that already existed. That's the one rule that has held the entire time: to make DNA, you need existing genetic material to copy from. Scientists just found a protein that breaks this rule. A mechanism nobody has seen before "It was quite a surprise!" Alex Gao, a biochemist at Stanford University in California and senior author of the study, told DW. His team had been investigating how bacteria protect themselves from viruses when they identified something unexpected: a protein called Drt3b that builds DNA without anything to copy from. It uses its own shape as a mold to snap the right building blocks into place. "We didn't believe it until we saw the cryo-EM structure [...] That was the moment it really clicked for us," he said — referring to cryo-electron microscopy, a technique that images molecules at near-atomic resolution. The findings were published in the journal Science in April. Gao and his team used the bacterium E. coli, found in the intestines of humans and other warm‑blooded animals. It is a cornerstone of research because of its fast growth and simple, well‑mapped genetics Image: NIH/IMAGE POINT FR/picture alliance So how does it actually work?
DRT3 — the full system studied by Gao's team — works in two steps. DNA is double-stranded: think of it like a zipper, with two sides that fit together. One side is built in a familiar way, with a protein called Drt3a using a small piece of genetic material as a template to build one strand. The other side is where things get strange. A second protein, Drt3b, needs to build the other side of that zipper — but does so without a template. Instead, specific parts of the protein itself act as the guide, locking onto the right DNA building blocks or "nucleotides" one by one until the strand is complete. And that's what we didn't think was possible — at least not like this. Other proteins have done something similar before — but only in short fragments, like writing a sentence. Drt3b writes a whole paragraph. It's the first known protein to produce a long, sequence-specific strand of DNA using nothing but its own structure as a guide. Why does it matter? "The research is groundbreaking," said Philip Kranzusch, a biochemist at Harvard Medical School who was not involved in the study. That’s because scientists have been studying DNA since the 1950s and bacteria have been quietly doing something they never imagined was possible. Which raises the question: what else are we missing? There's also a practical angle. If scientists could engineer Drt3b to produce other DNA sequences, it might one day work as a tool for building custom DNA molecules — without needing a template to copy from. But we're not there yet.
The BriefWire