Of Fireflies and Tobacco Plants

It sounds like a child's riddle: What do you get when you cross a firefly with a tobacco plant? Answer: tobacco that lights itself. That is essentially what a team of scientists at the University of California at San Diego has done. By outfitting a fragment of a plant virus with the gene that tells firefly cells to produce a protein central to generating light, the researchers have created a plant that literally glows in the dark.

The technique, reported in last week's issue of the journal Science, is significant not so much as a demonstration of virtuoso genetic engineering, but because it will provide scientists with a valuable research tool for studying how genes go about their business. By fusing the firefly gene to the genetic material of other plants and animals, biologists gain a visual cue $ that will help them understand in detail how genes -- strands of DNA whose structure acts as a sort of coded instruction manual -- tell different cells what their duties are within an organism. Armed with such specific knowledge, researchers may someday understand exactly why these instructions are occasionally garbled and, perhaps, why cancer and other gene-influenced diseases occur. Predicts Stephen Howell, a plant molecular biologist and a member of the research team: "The scientific community will be able to exploit this tool for as many purposes as one can imagine."

In studying genes, scientists deal basically with two components: one part supplies the code for the production of a particular protein, and the other, a sort of regulatory switch, turns the protein-producing mechanism on and off. In the human body, as in all organisms, every cell contains the complete genetic code and, in theory, has the potential to serve any function. A liver cell has the instructions necessary to grow hair, for example, and a bone cell to transmit information as a nerve does. The reason these things do not happen is that the instructions -- the genes -- are switched on only under very specific conditions. If researchers can fuse the firefly gene to specific plant or animal genes, they will be able to monitor the "expression," or turning on, of those genes simply by looking at what parts of the organism light up, and when.

The initial impetus for the research came from a rather oblique direction. UCSD Biochemist Marlene DeLuca has been investigating for 20 years how the firefly protein -- in this case, an enzyme called luciferase -- produces light. But the process of collecting and grinding up fireflies to extract the enzyme was laborious and costly. She and Donald Helinski, a molecular geneticist, decided to isolate the luciferase gene, cloning exact copies of it and splicing it into the genetic machinery of the common bacterium E. coli. The E. coli could then massproduce luciferase by the vat. DeLuca and Helinski accomplished this task by using standard recombinant DNA techniques developed over the past 20 years and now widely employed in industrial microbiology laboratories.