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See Inside April 2008

Double-Helix Double Up

Identical DNA strands recognize one another from afar

Talk about spooky action at a distance. Without any other molecules to guide them, double helices of DNA with identical sequences can recognize one another from a distance and even gather together.

That DNA bases attract is not a surprise, because base pairs are complementary like right- and left-handed gloves: adenine binds with thymine, cytosine with guanine. But when bound in a double-helix form, these bases are tucked away, hidden behind highly electrically charged strings of sugars and phosphates.

Nevertheless, scientists at Imperial College London and the U.S. National Institute of Child Health and Human Development found that double-stranded DNA with the same sequences were about twice as likely to come together as DNA with different sequences, from a distance of up to three nanometers. (Double-stranded DNA is about two nanometers wide.)

The researchers conjecture that the bases within each DNA cause a double helix to kink one way or the other. Although each DNA’s electrically charged groups of sugars and phosphates repel those on other DNA double helices, identical molecules have matching curves. As such, whereas all double-stranded DNA molecules repel one another somewhat, the ridges and grooves of identical helices fit together better than with those of other DNA, making it easier for like to cluster with like.

This attraction might help gene fragments align properly before they get shuffled about, perhaps aiding the careful weaving of DNA that occurs during reproduction. It might also ward off some of the genetic errors that underlie cancer and aging. For more, strand yourself in the January 31 Journal of Physical Chemistry B.

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