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.

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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?