DNA Element with a Murky Past is Borrowing Cell's Repair Machinery
Published:11 Oct.2023 Source:Duke University
Like its viral cousins, a somewhat parasitic DNA sequence called a retrotransposon has been found borrowing the cell's own machinery to achieve its goals. The finding upends 40 years of conventional wisdom saying these rings were just a useless by-product of bad gene copying.
Retrotransposons are segments of DNA around 7,000 letters long that copy and paste themselves into different parts of the genomes of both plants and animals. By doing this, they play a role in rewriting DNA and regulating how the cell uses its genes. Retrotransposons are believed to be behind a lot of the variation and innovation in genes that drives evolution, and are inherited from both parents. Retrotransposons are quite common -- they make up about 40% of the human genome, and more than 75% of the maize genome -- but how and where they copy themselves has always been a bit murky.
In the latest work, they found unexpectedly that most newly added retrotransposons were in this circular form rather than being integrated into the host's genome. Then they ran a series of experiments knocking out the cell's DNA repair mechanisms one at a time to figure out how and where the circles are being formed. The answer: A little-studied DNA repair mechanism called alternative end-joining DNA repair, or alt-EJ for short, which repairs doubles-stranded breaks. The discovery actually overturns the textbook model.