Study shows how cells prevent harmful extra copies of DNA

Study shows how cells prevent harmful extra copies of DNA

Study shows how cells prevent harmful extra copies of DNA

Graphically Abstract. Credit: molecular cell (2023). DOI: 10.1016/j.molcel.2022.12.004

A protein that prepares DNA for replication also prevents the replication process from getting out of hand, according to a new study by Weill Cornell Medicine researchers. The work, published on January 5 in molecular cellsolves a mystery that has long intrigued biologists.

The cells of humans and all other higher organisms use a complex system of checkpoints and “license” proteins to ensure that they accurately replicate their genomes once before dividing. In preparation for cell division, the licensing proteins attach to specific regions of the DNA, designating them as origins of replication. When the DNA synthesis phase of the cell cycle begins, replication begins only at authorized sites and is only initiated or “fired” once, depending on the current model.

However, that model was missing a crucial point. “The very factor that allows this license to occur is only degraded after these origins of replication are activated,” said lead author Dr. Tobias Meyer, the Joseph Hinsey Professor of Developmental and Cell Biology at Weill Cornell Medicine. “In principle, the cell could load these licensing machines into DNA that has already been replicated, so instead of two copies, you get three or four copies of that segment of DNA, and you expect these cells to lose the integrity of the genome and die or become cancerous.

Figuring out how cells avoid that fate has been tricky. “We needed to study events in the first few minutes of the DNA synthesis phase of the cell cycle, so it’s a very transitory period,” said first author Nalin Ratnayeke, a graduate student who worked on this project at both Stanford University and in Weill. Cornell Medicine in Dr. Meyer’s lab.

The lab moved to Weill Cornell Medicine in 2020. To solve this difficult experimental problem, Ratnayeke used computer-assisted microscopy to monitor thousands of growing cells simultaneously, capturing replicating cells in the act and analyzing the activities of their licensing factors. and replication.

The work revealed that a well-known licensing factor, CDT1, not only licenses a segment of DNA to become an origin of replication, but also acts as a brake on DNA replication, preventing an enzyme from working. essential replication agent called CMG helicase. To start synthesizing DNA, enzymes in the cell must first break down CDT1.

“Previously proposed mechanisms for coordinating this transition from the licensing phase of the cell cycle to the activation phase of the cell cycle have relied on the inhibition of licensing factors,” Ratnayeke said, adding that “the mechanism we identified here is in The opposite is true… The CDT1 licensing factor itself is preventing the progression of DNA synthesis.”

To confirm their results, the scientists collaborated with colleagues at the Medical Research Council in Cambridge, UK, who discovered that the inhibitory mechanism can be recapitulated into a simplified system that replicates the entire process of DNA synthesis with purified components in a tube of rehearsal.

“That allowed us to reconstitute all the components for DNA synthesis and show that CDT1 directly inhibits CMG helicase,” said Dr. Meyer, who is also a professor of biochemistry and a member of the Sandra and Edward Meyer Cancer Center in WeillCornell Medicine. .

Because replication license failures can kill cells or make them cancerous, the results provide a new understanding of cell health and disease. “Future work to mechanistically identify what is happening with Cdt1 inhibition will provide further insight into the biophysics of how CMG helicase works, and pinpoint specific regions of this complex that can be targeted with drugs,” Ratnayeke said.

More information:
Nalin Ratnayeke et al, CDT1 inhibits CMG helicase in early S phase to separate DNA synthesis origin license, molecular cell (2023). DOI: 10.1016/j.molcel.2022.12.004

Provided by Weill Cornell Medical College

Citation: Study shows how cells prevent harmful extra copies of DNA (Jan 24, 2023) Retrieved Jan 24, 2023 from https://phys.org/news/2023-01-cells-extra-dna.html

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