DNA and the 'magic rings' trick

Oct 11, 2010

(PhysOrg.com) -- A new study from UC Davis shows how, like a conjuring trick with interlocking rings, two interlocked pieces of DNA are separated after DNA is copied or repaired. The finding was published online Oct. 10 in the journal Nature Structural and Molecular Biology.

While reconstituting the DNA repair system of yeast in a test tube, the researchers found that a complex of proteins called Sgs1, Top3 and Rmi1 allow one DNA strand to open and the other to pass through.

"This protein complex does what magicians do," said lead researcher Stephen Kowalczykowski, distinguished professor of microbiology in the UC Davis College of Biological Sciences and a member of the of the UC Davis Cancer Center.

The discovery may hold answers to a human disease called Bloom's syndrome, which increases the risk of cancer, among other health problems. Sgs1 appears to be the yeast equivalent of the human protein tied to Bloom's syndrome, Kowalczykowski said.

DNA suffers damage all the time both from outside influences, such as radiation or chemicals, and also from normal cellular processes. Unrepaired, can lead to cancer or birth defects. Several genes linked to a high risk of cancer, such as the " gene" , have turned out to be involved in DNA repair.

When damage crosses both strands of the , a sophisticated repair process is activated that uses the same DNA sequence on the matching chromosome. One of the strands is stripped back, leaving an exposed single strand. The matching chromosome is brought alongside and partly unwound, and acts as a template to repair the broken piece.

At this point, the two are intact but attached at two points through structures called "Holliday junctions," where DNA strands from the two chromosomes cross each other. To finish the process, the chromosomes have to separate -- like the magician's interlocking rings, one has to pass through the other.

Working with a mix of yeast proteins and DNA in a test tube, Kowalczykowski and his colleagues showed that the Sgs1/Top3/Rmi1 protein complex attaches to the paired DNA at the Holliday junction, opens up a gap in one strand and passes the other through it, allowing the two chromosomes to separate cleanly and dissolving the junction.

Patients with Bloom's syndrome show extensive swapping of chunks of DNA between chromosomes. Kowalczykowski is convinced that the problem is due to poor dissolution of Holliday junctions in these patients.

Holliday junctions were only definitively shown to exist in mitotically dividing cells in April this year, in a paper by UC Davis researchers Malgosia Bzymek and Neil Hunter, associate professor of microbiology.

Kowalczykowski’s collaborators in the new study were UC Davis postdoctoral researchers Petr Cejka and Jody Plank, and Oxford University scientists Csanad Bachrati and Ian Hickson.

In a paper published in Nature last month, Kowalczykowski's lab also showed that the Sgs1/Top3/Rmi1 complex of proteins is involved in the first step of -- cleaning the broken end to leave a single strand of DNA.

Explore further: Life's extremists may be an untapped source of antibacterial drugs

Related Stories

Unknotting DNA clue to cancer syndrome

Aug 03, 2007

A new UC Davis study that explains the actions of a gene mutation that causes early onset cancer provides a fundamental insight into the mechanism of DNA-break repair.

Study Confirms DNA Repair Model After 26 Years

Apr 14, 2010

(PhysOrg.com) -- UC Davis researchers have confirmed a central idea about chromosome repair, more than a quarter century after it was first proposed. The finding is important to scientists who seek to understand DNA repair, ...

Protein made by breast cancer gene purified

Aug 22, 2010

A key step in understanding the origins of familial breast cancer has been made by two teams of scientists at the University of California, Davis. The researchers have purified, for the first time, the protein produced by ...

Understanding DNA Repair and Cancer

Dec 03, 2009

(PhysOrg.com) -- A protein that plays a key role in copying DNA also plays a vital role in repairing breaks in it, UC Davis scientists have found. The work is helping researchers understand how cancer cells can resist radiation ...

Human DNA repair process recorded in action (Video)

Jan 29, 2009

(PhysOrg.com) -- A key phase in the repair process of damaged human DNA has been observed and visually recorded by a team of researchers at the University of California, Davis. The recordings provide new information ...

Recommended for you

Cohesin molecule safeguards cell division

Nov 21, 2014

The cohesin molecule ensures the proper distribution of DNA during cell division. Scientists at the Research Institute of Molecular Pathology (IMP) in Vienna can now prove the concept of its carabiner-like ...

Nail stem cells prove more versatile than press ons

Nov 21, 2014

There are plenty of body parts that don't grow back when you lose them. Nails are an exception, and a new study published in the Proceedings of the National Academy of Sciences (PNAS) reveals some of the r ...

Scientists develop 3-D model of regulator protein bax

Nov 21, 2014

Scientists at Freie Universität Berlin, the University of Tubingen, and the Swiss Federal Institute of Technology in Zurich (ETH) provide a new 3D model of the protein Bax, a key regulator of cell death. When active, Bax ...

Researchers unwind the mysteries of the cellular clock

Nov 20, 2014

Human existence is basically circadian. Most of us wake in the morning, sleep in the evening, and eat in between. Body temperature, metabolism, and hormone levels all fluctuate throughout the day, and it ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

kevinrtrs
1 / 5 (6) Oct 12, 2010
When damage crosses both strands of the DNA double helix, a sophisticated repair process is activated that uses the same DNA sequence on the matching chromosome.


If it hasn't become clear before, now it should be crystal clear that the Darwinian evolutionary thought of random mutations and "natural selection" being responsible for molecules to man evolution is just so much chaff in the wind.

Any kind of repair system flies in the face of [m-2-m] evolution because it points out that there's forethought involved which recognizes that damage is likely to occur and then set out to PREVENT that damage from causing harm to the organism.

It's only after the separation of earth life from their creator that inevitable damage was actually allowed to continue unabated.

Skeptic_Heretic
5 / 5 (3) Oct 12, 2010
If it hasn't become clear before, now it should be crystal clear that the Darwinian evolutionary thought of random mutations and "natural selection" being responsible for molecules to man evolution is just so much chaff in the wind.
Only to those who don't understand it due to either childhood indoctrination or extreme inability to use logic and reason.
Any kind of repair system flies in the face of [m-2-m] evolution because it points out that there's forethought involved which recognizes that damage is likely to occur and then set out to PREVENT that damage from causing harm to the organism.
Seeing as the non-random survival of randomly generated organisms is the whole of natural selection, one would assume that logically you'd understand that a self-repairing system will have a greater chance of survival than a non-repairing system.
It's only after the separation of earth life from their creator
The same creator who created the vectors for damage?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.