Light-sensitive proteins are useful tools to control protein localization, activation and geneexpression, but are currently limited to excitation with red or blue light. Here we report anovel optogenetic system based on the ultraviolet-B-dependent interaction of the Arabidopsisultraviolet-B photoreceptor UVR8 with COP1 that can be performed in visible lightbackground. We use this system to induce nuclear accumulation of cytoplasmic greenfluorescent protein fused to UVR8 in cells expressing nuclear COP1, and to recruit anucleoplasmic red fluorescent protein fused to COP1 to chromatin in cells expressingUVR8-H2B. We also show that ultraviolet-B-dependent interactions between DNA-bindingand transcription activation domains result in a linear induction of gene expression.The UVR8–COP1 interactions in mammalian cells can be induced using subsecond pulses ofultraviolet-B light and last several hours. As UVR8 photoperception is based on intrinsictryptophan residues, these interactions do not depend on the addition of an exogenouschromophore.
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