Protein-protein interactions are essential for many cellular processes. We have 
developed a technology called light-activated dimerization (LAD) to artificially 
induce protein hetero- and homodimerization in live cells using light. Using the 
FKF1 and GIGANTEA (GI) proteins of Arabidopsis thaliana, we have generated 
protein tags whose interaction is controlled by blue light. We demonstrated the 
utility of this system with LAD constructs that can recruit the small G-protein 
Rac1 to the plasma membrane and induce the local formation of lamellipodia in 
response to focal illumination. We also generated a light-activated 
transcription factor by fusing domains of GI and FKF1 to the DNA binding domain 
of Gal4 and the transactivation domain of VP16, respectively, showing that this 
technology is easily adapted to other systems. These studies set the stage for 
the development of light-regulated signaling molecules for controlling receptor 
activation, synapse formation and other signaling events in organisms.