Summary: We present here PhotoGal4. a phytochrome B-based optogenetic switch for fine-tuned spatiotemporal control of gene expression in Drosophila explants. This switch integrates the light-dependent interaction between phytochrome B and PIF6 from plants with regulatory elements from the yeast Gal4/UAS system. We found that PhotoGal4 efficiently activates and deactivates gene express... https://www.roneverhart.com/Viking-K2-Slide-Gate-Opener-SPS-Model/