Scientists have a new way to watch genes in action.
One plant can detect another up to a metre away by the light its leaves reflect. Now researchers have exploited this natural light-detection system to make a switch that turns genes on and off just when they want - creating a way of watching the effect of a gene at any time or place1.
Peter Quail and colleagues at the University of California, Berkeley, have made yeast cells that turn blue after exposure to a flash of red light but which return to a less colourful state under a burst of far-red light. A similar technique should work in animal cells to study the expression of practically any gene that researchers choose as simply as turning on a light.
At present, scientists use chemicals or heat to activate a gene at particular times or in a particular tissue in genetically modified animals such as fruitflies or mice. Light is much less invasive and can even be targeted to a single cell.
Plants detect light using proteins called phytochromes. These exist in two states, known as Pr and Pfr. When red light falls on a phytochrome in the Pr state it changes to the Pfr form. Light just off the red end of the visible spectrum converts it back again.
Quail's team capitalize on one of the many effects of this change. Pfr phytochromes stick to a protein called PIF3, but Pr phytochromes don't.
Working with yeast, the researchers attached one half of GAL4, a protein that turns on genes by binding to sites in their DNA, to one end of phytochrome B. The other half they attached to PIF3.
The two halves of GAL4 come together when phytochrome B binds PIF3 under the influence of light. Then GAL4 can bind to genes containing the GAL4 promoter, causing production of the proteins that these genes encode.
In the test case, the gene coded for a protein called beta-glactosidase, which turns the yeast cells blue.
Christopher Surridge is a Senior Biological Sciences Editor on the journal Nature.
Quail, P.H. A light switchable gene promoter system. Nature Biotechnology, published online, doi:10.1038/nbt734 (2002).