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Four-strand DNA structure found in cells 2013-01-25 0:00
Unusual nucleic-acid structure may have role in regulating some genes.
There is no more iconic image in biology than that of DNA’s double-stranded helix, which coils and supercoils on itself to form dense chromosomes.
But a quite different, square-shaped type of DNA structure can easily be created in the laboratory by the folding of synthetic DNA strands rich in guanine, one of the building blocks of DNA. Scientists have long believed that these so-called ’G-quadruplex structures’ may occasionally form in the DNA of living cells. A G-quadruplex comprises four guanines from different places along a G-rich strand held together by a special type of hydrogen bonding to form a compact square structure that interrupts the DNA helix.
In a paper published online today in Nature Chemistry1, researchers led by Shankar Balasubramanian at the University of Cambridge, UK, provide strong evidence that G-quadruplexes do occur in cells — and that these unusual structures may have important biological functions.
A representation of the four-stranded structure (L) with fluorescent markers revealing its presence inside cells (R)
Protecting the chromosome
The protective tips of chromosomal DNA, known as telomeres, are rich in guanine and so are likely candidates for G-quadruplex structures. In fact, studies in cancer cells have shown that small molecules that bind and stabilize G-quadruplex structures cause DNA damage at telomeres, supporting the argument2.
After trawling through human genome data in search of other guanine-rich sequences, some scientists have suggested that quadruplexes could also be created in other areas of the genome involved in regulating genes, particularly some cancer-causing genes.
This seems likely to be the case, Balasubramanian and colleagues found. They engineered an antibody that binds tightly and specifically to G-quadruplex structures and does not bind to double-stranded helical DNA. When they incubated the antibody with human cells in culture, they found that it bound to many different sites in the chromosomes, only around a quarter of them in telomeres.
“It’s early days, but if we can map exactly where these G-quadruplex structures pop up in the genome, we may learn how better to control genes or other cellular processes that go awry in diseases like cancer,” he says. “That’s the long-term vision anyway.’’
Russians drop leaflets on ISIS, implying America and Israel is behind them 2015-10-09 4:38
Dire warning: The leaflets (pictured) being dropped by Russian jets warn people to get out of the zone of 'special operations' - and one implies that terror group al-Nusra Front are backed by America and Israel
Syrian army helicopters have dropped tens of thousands of leaflets on ISIS and rebel fighters, warning them to get out now and 'don't make it even ...
College diversity officer charged for #KillAllWhiteMen tweet 2015-10-08 23:16
A U.K. college diversity officer’s utopia would include no white men – after they are all executed.
An employee of Goldsmiths University of London’s independent students’ union was arrested in London Tuesday and charged with sending a menacing or offensive messages via a public network for her “#killallwhitemen” tweets.
Bahar Mustafa, 28, faces one charge each for electronic communications she sent over ...
Paedo deported from UK sneaked back and worked with kids for two years before being caught 2015-10-08 23:50 Landazuri worked with teenagers for two years before he was caught
Juan Guerra Landazuri successfully lived in Britain with his new identity for two years and even got a job helping vulnerable teenagers - despite being banned from working with children for life.
The 44-year-old, originally known as Juan Alejandro Guerra, was jailed for four years in 2002 for two offences of ...
Why Don't More Minorities Hike? 2015-10-08 23:06
As a Bay Area native, I grew up in outdoor spaces. While hiking trails in Tilden Park in the East Bay and in the Marin Headlands in the North Bay, I gained an appreciation of and respect for natural spaces that eventually led me to visit our national parksâ€”Yosemite being my favorite.
It was in Yosemite that I started to notice ...