UCSF

Genetically-encodable optical reporters, such as Green Fluorescent Protein, have revolutionized the observation and measurement of cellular states. However, the inverse challenge of using light to precisely control cellular behavior has only recently begun to be addressed; in recent years, semi-synthetic chromophore-tethered receptors and naturally-occurring channel rhodopsins have been used to directly perturb neuronal networks. The difficulty of engineering light sensitive proteins remains a significant impediment to the optical control to most cell-biological processes. I have focused my work over the last five years on the production of genetically-encoded light-sensitive reagents for the control of both bacterial and eukaryotic signalling networks. I have demonstrated minute-timescale control of bacterial transcriptional networks with engineered light-sensitive histidine kinases. I have also demonstrated the use of a new genetically encoded light-control system based on an optimized reversible protein-protein interaction from the phytochrome signaling network of Arabidopsis thaliana. Because protein-protein interactions are one of the most general currencies of cellular information, this latter system can in principal be generically used to control diverse functions. I show that this system can be used to precisely and reversibly translocate target proteins to the membrane with micrometer spatial resolution and second time resolution. I show that light-gated

translocation of the upstream activators of rho-family GTPases, which control the actin cytoskeleton, can be used to precisely reshape and direct the cell morphology of mammalian cells. The light-gated protein-protein interaction that has been optimized in this latter work should be useful for the design of diverse light-programmable reagents, potentially enabling a new generation of perturbative, quantitative experiments in cell biology.