ReaChR is a light-gated cation channel that can be used as an optogenetic tool to activate neurons; it is optimally excited by red light of wavelength 590-630nm. ReaChR is an artificial channelrhodopsin that combines sequence from three different naturally occurring channelrhodospin genes; VChR1 and VChR2 from Volvox carteri, and ChR1 from Chlamydomonas reinhardtii. It consists of the extracellular N-terminus from ChIEF (originates from ChR1), transmembrane domains A-E and G of VChR1, transmembrane domain F of VChR2 and a L171I point mutation in transmembrane domain C (PMID:23995068). The formation of a functional channel requires the presence of a covalently linked all-trans-retinal chromophore which can be provided exogenously if necessary via the culture medium or diet (this cofactor is present endogenously in some intact vertebrate systems). For detailed kinetic and spectral properties, see PMID:23995068.