Sequencing DNA using remote Braille.

Sequencing DNA using remote Braille

Using the fine tip of a scanning tunneling microscope as a teensy surrogate finger for feeling and recording the atomic bumps and valleys of molecules, two chemists have reconstructed images of synethic strands of DNA. In the Nov. 9 NATURE, David D. Dunlap and Carlos Bustamante of the University of New Mexico in Albuquerque suggest they may be able to improve the techique enough to enable geneticists to directly determine the sequence of nucleotide building blocks that make up strands of DNA. They envision looking at graphic reconstructions of the strands and reading off the nucleotides like letters in a sentence. DNA sequencing presently involves time-consuming and less direct biochemical techniques.

In their experiment, the New Mexico scientists coated a specially prepared graphite surface with a single layer of polydeoxyadenylate molecules, or poly(dA)--chain-like DNA molecules composed solely of the nucleotide building block deoxyadenylate. The researchers produced images that clearly show the constituent nucleotides' two chemical rings attached to an equally visible molecular backbone of poly(dA) strands.

Impressive as the images are, the researchers say they still aren't clear enough to allow investors to distinguish among all four nucleotides in the more complicated DNA molecules in cells. Other hurdles include rendering each of a DNA strand's many nucleotides completely accessible to the tip of the scanning tunneling microscope and preventing more complicated and often complementary DNA strands from forming into double strands once they deposit onto the graphite surface.