Researchers at the University of North Carolina in Chapel Hill and the Max Planck Institute in Heidelberg, Germany have genetically engineered animal cells to make proteins that can be turned on and off using visible light.

The researchers spliced a gene for a light-activated protein with the gene for a protein called Rac, which is known to be involved in regulating healthy cell movements as well as the movement of cancer cells. Researchers then focused laser light to locally activate the proteins, causing protrusions that led to cell movement. The work was described this week in the journal Nature.

The location of a protein within the cell plays a role in determining the cell’s behaviors, but this has been difficult to study. The researchers hope using light activation will be a good method.

Here’s how it works: the light-activated portion of the protein blocks the binding site on Rac. When it’s illuminated, the block is removed and Rac can function. A second pulse of light at a different wavelength causes the block to move back into position, deactivating the protein.

The technique should be compatible with other proteins in addition to Rac. In the past, researchers have made proteins that are activated by ultraviolet radiation, which is toxic to cells. And these previous proteins couldn’t be turned off again; the new ones can.