For the first time, microscopic robots made from DNA molecules can walk, follow instructions and work together to assemble simple products on an atomic-scale assembly line, mimicking the machinery of living cells, two independent research teams announced Wednesday.

These experimental devices, described in the journal Nature, are advances in DNA nanotechnology, in which bioengineers are using the molecules of the genetic code as nuts, bolts, girders and other building materials, on a scale measured in billionths of a meter. The effort, which combines synthetic chemistry, enzymology, structural nanotechnology and computer science, takes advantage of the unique physical properties of DNA molecules to assemble shapes according to predictable chemical rules.

Until now, such experiments had yielded molecular novelties, from smiley faces so small that a billion can fit in a teaspoon to molecule-size boxes with lids that can be opened, closed and locked with a DNA key.

These new construction projects bring researchers a step closer to a time when, at least in theory, scientists might be able to build test-tube factories that churn out self-assembling computers, rare chemical compounds or autonomous medical robots able to cruise the human bloodstream.