Showing by glowing.

Showing by glowing

Meanwhile, back at the genetic level of development: Researchers have found a way to tag gene products with light, making it possible to watch as genes on chromosomes in living organisms are turned on and off.

The researchers, at Texas A&M University in College Station and the Boyce Thompson Institute for Plant Research in Ithaca, N.Y., used genes that code for a light-producing enzyme called luciferase, from a glowing saltwater bacterium. They fused the luciferase genes to promoter sequences (essentially, "on' switches) of nitrogen-fixation genes, and inserted the engineered DNA into a nitrogen-fixing bacterium that lives symbiotically with soybean plants. "When the soybean plant calls for nitrogen,' says Thomas Baldwin of Texas A&M, "the root nodules light up.'

This method of gene-tagging has advantages over previous ones, Baldwin says. The assay is much more sensitive, capable of detecting single photons from single molecules of gene product. The assay does not disturb the living system, so biological processes can be monitored. (While some other markers can be assayed in vivo, they are generally "extremely cumbersome' techniques, Baldwin says.) And, since the substrate for the luciferase enzyme is present in nearly every living organism, the marker may be a way to study gene activity in higher organisms. The technique will be described in an upcoming PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES.