ChR2 corresponds to a light-gated cation channel derived from the Chlamydomonas reinhardtii Channelrhodopsin-2 gene (GB:AF461397). It can be used as an optogenetic tool to activate neurons; the peak activation wavelength is approximately 460nm. The seven-transmembrane (7TM) region encoded by the N-terminal half of the Channelrhodopsin-2 gene is sufficient for the ion conductance, as the full-length protein and a truncated version encoding the first 315 amino acids show identical photocurrents and very similar current-voltage relationships (PMID:14615590). 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 properties, see PMID:19254539 and PMID:22179551. For a comparison of ChR2 and other neuron activation tools, see PMID:20621963 and PMID:22179551.