A protein that prepares DNA for replication also prevents the replication process from running out of control, according to a new study. The study, published in Molecular Cell, solves a mystery that has long puzzled biologists.
The cells of humans and all other higher organisms use a complex system of checkpoints and “licensing” proteins to ensure that they replicate their genomes precisely once before dividing. In preparation for cell division, the licensing proteins attach to specific regions in the DNA, designating them as replication origins. When the DNA synthesis phase of the cell cycle begins, replication begins only at those licensed sites, and only initiates, or “fires” once, according to the current model.
That model was missing a crucial point, though. “The same factor that is allowing for this licensing to happen is only degraded after these replication origins have fired,” said senior author. “In principle, the cell could load these licensing machines onto DNA that’s already replicated, so, instead of two copies, you’re getting three or four copies of that segment of the DNA, and these cells would be expected to lose genome integrity and die or become cancerous.”
Figuring out how cells avoid that fate has been tricky. “We needed to be studying events in the first minutes of the DNA synthesis phase of the cell cycle, so it’s a very transient period,” said the first author. To solve this difficult experimental problem, the authors used computer-aided microscopy to monitor thousands of growing cells simultaneously, catching the replicating cells in the act and analyzing the activities of their licensing and replication factors.
The work revealed that a well-known licensing factor, CDT1, not only licenses a segment of DNA to become a replication origin, but also acts as a brake for DNA replication, preventing an essential replication enzyme called CMG helicase from functioning. To start synthesizing DNA, the cell’s enzymes must first break down CDT1. “Previously proposed mechanisms for coordinating this transition from the licensing phase of the cell cycle to the firing phase of the cell cycle have depended on inhibiting licensing factors,” said the author, adding that “the mechanism that we identified here is actually the opposite … the licensing factor CDT1 itself is preventing the progression of DNA synthesis.”
To confirm their results, the scientists collaborated with colleagues at UK, who found that the inhibitory mechanism can be recapitulated in a simplified system that reproduces the entire DNA synthesis process with purified components in a test tube. “That allowed us to reconstitute all the components for DNA synthesis, and to prove that CMG helicase is directly inhibited by CDT1,” said the senior author.
Because failures in replication licensing can kill cells or make them cancerous, the results provide a new understanding of cell health and disease. “Future work to identify mechanistically what’s going on with Cdt1 inhibition will give greater insight into the biophysics of how CMG helicase functions, and will pinpoint specific regions of this complex that can be targeted using drugs,” said the first author.
https://www.cell.com/molecular-cell/fulltext/S1097-2765(22)01161-3
How cells prevent harmful extra DNA copies
- 920 views
- Added
Latest News
Mechanism of sugar signalin…
By newseditor
Posted 19 May
How does the brain turn wav…
By newseditor
Posted 19 May
A trial HIV vaccine trigger…
By newseditor
Posted 19 May
AI to predict DNA methylati…
By newseditor
Posted 19 May
Hyperactive platelets from…
By newseditor
Posted 19 May
Other Top Stories
A brain circuit inhibits food intake during nausea
Read more
Link between dietary choices and brain health
Read more
Circadian clock synchronization between brain and muscle prevents m…
Read more
Genomic regions with epigenetic modifications linked to ALS progres…
Read more
Males burn more fat, while females recycle it during exercise
Read more
Protocols
Breast cancer-on-chip for p…
By newseditor
Posted 16 May
Methods for making and obse…
By newseditor
Posted 15 May
Mime-seq 2.0: a method to s…
By newseditor
Posted 13 May
Improved detection of DNA r…
By newseditor
Posted 09 May
Single-cell adhesive profil…
By newseditor
Posted 07 May
Publications
Molecular mechanism of treh…
By newseditor
Posted 19 May
Hue selectivity from recurr…
By newseditor
Posted 19 May
Vaccine induction of hetero…
By newseditor
Posted 19 May
Brain border-associated mac…
By newseditor
Posted 19 May
Inhibition of fatty acid up…
By newseditor
Posted 19 May
Presentations
Hydrogels in Drug Delivery
By newseditor
Posted 12 Apr
Lipids
By newseditor
Posted 31 Dec
Cell biology of carbohydrat…
By newseditor
Posted 29 Nov
RNA interference (RNAi)
By newseditor
Posted 23 Oct
RNA structure and functions
By newseditor
Posted 19 Oct
Posters
A chemical biology/modular…
By newseditor
Posted 22 Aug
Single-molecule covalent ma…
By newseditor
Posted 04 Jul
ASCO-2020-HEALTH SERVICES R…
By newseditor
Posted 23 Mar
ASCO-2020-HEAD AND NECK CANCER
By newseditor
Posted 23 Mar
ASCO-2020-GENITOURINARY CAN…
By newseditor
Posted 23 Mar