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17 April 2014 12:48 pm ,
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Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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Unzip Your Genes
7 November 1997 8:00 pm
If you think trying to unzip your coat while wearing mittens is hard, try undoing that most famous of zippered molecules, double-stranded DNA. Now, for the first time, scientists have been able to use something akin to molecular tweezers to pry apart a DNA molecule. The feat, described in the current issue of the Proceedings of the National Academy of Sciences, could lead to a faster method of finding hidden genes in unexplored DNA.
Two years ago, biophysicists succeeded in measuring the force exerted by a single molecule of RNA polymerase as it moves along a single DNA strand, reading the genetic code (Science, 8 December 1995, p. 1653). That inspired physicist François Heslot and his colleagues at the École Normale Supérieure in Paris to devise a way to measure the force required for the polymerase to unzip a DNA double helix into two strands.
The researchers designed a 30-micrometer-long stretch of DNA with two small proteins stuck on at strategic places. One protein anchored one end of the DNA to a specially coated glass slide. They also created a break in one of the two strands, halfway up the DNA, and attached the other "sticky" protein onto a loose end of the broken strand. That protein attached itself tightly to a floating, coated microbead. When the researchers touched a microneedle to the sticky bead and slowly slid the glass slide, the tension peeled apart the DNA strands.
The needle's tension, revealed by how much it bent, roughly matched the pattern of DNA base pairs whose bonds keep the helix together. The DNA would pull apart more easily in stretches dominated by adenosine and tyrosine, compared to those with more cytosine and guanine pairs, which are known to bind more tightly.
Because the beginnings of many gene sequences are rich in cytosine and guanine, measuring subtle changes in tension during DNA unzipping could be a promising method for quickly spotting genes in virgin DNA territory, according to Heslot. For now, however, Heslot's microneedle can only gauge differences in tension over several hundred base pairs, although the team thinks it can improve the resolution to every 20 base pairs. That would allow researchers to get "a very quick view" of the sequence, Heslot says, so they can concentrate on smaller sections of interest and avoid the time and cost of sequencing every base.
The technique might also help biophysicists better study how DNA is translated into the RNA that makes proteins. "Basically all of molecular genetics is based on getting strands apart, reading strands, putting strands back together," says John Marko of the University of Illinois, Chicago. "Now we can pull strands of double helix apart in the test tube under very controlled conditions."