The present palette of opsin-based optogenetic tools lacks a light-gated 
potassium (K(+)) channel desirable for silencing of excitable cells. Here, we 
describe the construction of a blue-light-induced K(+) channel 1 (BLINK1) 
engineered by fusing the plant LOV2-Jα photosensory module to the small viral 
K(+) channel Kcv. BLINK1 exhibits biophysical features of Kcv, including K(+) 
selectivity and high single-channel conductance but reversibly photoactivates in 
blue light. Opening of BLINK1 channels hyperpolarizes the cell to the K(+) 
equilibrium potential. Ectopic expression of BLINK1 reversibly inhibits the 
escape response in light-exposed zebrafish larvae. BLINK1 therefore provides a 
single-component optogenetic tool that can establish prolonged, physiological 
hyperpolarization of cells at low light intensities.