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Cambridge University Scientists Find Quadruple Helix DNA In Human Cells
SternisheFan notes that scientists at Cambridge University have found four-stranded DNA in human cells for the first time. "If you've ever studied genetics in school or college, you'll know that the structure of DNA is a double helix. You likely know that DNA carries all of our genetic code. While traditionally we think of only double helix DNA, scientists from Cambridge University in England have made an interesting discovery. According to the researchers, a quadruple helix is also present in some cells and is believed to relate to cancer in some ways. According to the researchers, controlling these quadruple helix structures could provide new ways to fight cancer. The scientists believe the quadruple helix may form when the cell has a certain genotype or operates in a certain dysfunctional state. Scientists have been able to produce quadruple helix material in test tubes for years. The material produced is called the G-quadruplex. The G refers to guanine, which is one of the base pairs that hold DNA together. The new research performed at the University is believed to be the first to firmly pinpoint quadruple helix in human cells."
...that "Guanine Quadruplex" works equally well as the name for either a band or a signature wrestling move.
The first annual Obfuscated DNA Contest
They found it in dividing cells. Cancer cells divide, which is the problem, as that causes tumors. I'm assuming they used multiple cell lines, some cancerous and some not, and found it present more in cancer cells than in normal cells.
It says they're also found in S phase cells, when the DNA is being replicated. This might contribute to cancer through genomic instability. There is a LOT of DNA to copy each cell cycle. The DNA polymerase is an impressive bit of evolved machinery, if each DNA base pair were the size of a railroad tie, the polymerase would be zipping along at a thousand miles an hour, copying the railroad tracks nearly perfectly as it does. It's also pretty good at catching its own mistakes. However, changes in the structure of DNA can cause a much higher frequency of errors in copying, and consequently, can increase the rates of mutation. It might skip copying a gene important for preventing the cell from dividing.
Perhaps most importantly though, these structures being present more in cancer cells than in normal cells means they might be good targets for identifying cells that are cancerous. Perhaps we can find a drug that directly or indirectly destroys those structures when they are present in such a way that the cell itself will be killed. That would be far more targeted than current chemotherapy, which attacks all dividing cells.
Big if of course. At this point, as far as published stuff goes, it's not yet to the point where it is going to lead to something useful in hospitals in the definite future.
Some portions of DNA are rich in Guanine residues. There's been a theory kicking around that these bits could form into tetromeres, which would make the two DNA strands extra sticky to each other. A number of really wierd phenotypes, including werner's syndrome which causes premature aging, can come from the inaccurate unfolding of G rich regions. Likewise the telomeres, ie the ends of the DNA which essentially work as a division counter are G-rich. As such, if the accurate unfolding, stability or stickyness of the DNA in these regions is affected, the cellular behavior will change.
The article went through using a phage library to build an antibody specific for 4 stranded DNA (NOT easy), which did not respond to 2-stranded DNA or RNA structures. They then looked at whether, when and where tetromeres could be seen in a bone cancer cell line. Oddly enough, the regions most likely to show these structures, the telomeres, didn't show tetromeres. These structures were seen when the cell was about to get ready to divide, which makes some sense, since the cell will have more DNA. (There's a fair bit of research currently going on to study DNA supercoiling- DNA is compacted down very tightly, yet almost all of it is accessible at any given time)
As far as curing cancer, any time you can isolate behavior of cancer-only cells, you have the ability to create a drug to target that function. If these tetromeres are seen only in cancerous cells, then you can design drugs against them. Beyond that, the folding and unfolding of DNA is a pretty hot topic, since volumetric compression, read speeds and accuracy are astonishing compared to even the best hard drives on the market