Second layer of information in DNA confirmed

A group of theorists from Leiden has shown that DNA physics, along with genetic information, decides who we are. His team imagined a lot of different DNA patterns and discovered a link between mechanical cues and the way DNA is folded. Their work has been published in PLoS One.

In 1953, James Watson and Francis Crick figured out the shape of DNA molecules. This showed that DNA information makes us who we are. Which proteins our cells make depend on the order of the letters G, A, T, and C in the familiar double helix. For example, the reason you have brown eyes is because of a set of letters in your DNA that code for proteins that make brown eyes. Even though every cell has the same set of letters, each organ acts in a different way. How is it possible?

Cues from machines

Since the middle of the 1980s, people have thought that DNA's mechanical features make up a second layer of information on top of the genetic code. There are two meters of DNA molecules inside each of our cells. These molecules have to be tightly wound up to fit inside a single cell. The letters are read out based on how the DNA is bent, which in turn decides which proteins are made. Only the parts of the DNA that are needed are read in each cell. The idea says that the way DNA folds is controlled by mechanical cues inside the DNA structures.

Playing Games

Helmut Schiessel, a physicist at Leiden, and his study group show for the first time that this second layer of knowledge does exist. With their computer code, they were able to model how DNA strands fold by giving them random mechanical cues. These clues do, in fact, control how the DNA helix folds into things called nucleosomes. Schiessel discovered links between the physics and the real folding structure in the genomes of two different types of organisms, called fission yeast and baker's yeast. This discovery shows that changes in DNA over time, called mutations, can have two very different outcomes: the letter sequence that codes for a certain protein can change, or the structure of the DNA can change, leading to different levels of DNA accessibility and packaging, which in turn leads to different rates of protein production.