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"Jumping genes"—bits of DNA that can move from one spot in the genome to another—are well-known for increasing genetic diversity over the long course of evolution. Now, new research at Washington University School of Medicine in St. Louis indicates that such genes, also called transposable elements, play another, more surprising role: stabilizing the 3-D folding patterns of the DNA molecule inside the cell's nucleus.
The study appears Jan. 24 in the journal Genome Biology.
DNA - Molecule - Nucleus - Cell - Feet
The DNA molecule inside the nucleus of any human cell is more than six feet long. To fit into such a small space, it must fold into precise loops that also govern how genes are turned on or off. It might seem counterintuitive that bits of DNA that randomly move about the genome can provide stability to these folding patterns. Indeed, the discovery contradicts a long-held assumption that the precise order of letters in the DNA sequence always dictates the broader structure of the DNA molecule.
"In places where the larger 3-D folding of the genome is the same between mice and humans, you expect the sequence of the letters of the DNA anchoring that shape to be conserved there as well," said senior author Ting Wang, Ph.D., the Sanford C. and Karen P. Loewentheil Distinguished Professor of Medicine. "But that's not what we found, at least not in the portions of the genome that in the past have been called 'junk DNA.'"
DNA - Folding - Mouse - Blood - Cells
Studying DNA folding in mouse and human blood cells, the researchers found that in many regions where the folding patterns of DNA are conserved through evolution, the genetic sequence of the DNA letters establishing these folds is not. It is ever so slightly displaced. But this changing sequence, a genetic turnover, doesn't cause problems. Because the structure largely stays the same, the function presumably does, too, so...
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