C1V1(E122T.E162T) is a light-gated cation channel that can be used as an optogenetic tool to activate neurons; it is optimally excited by light of 535nm wavelength. C1V1(E122T.E162T) is an artificial channelrhodopsin that combines sequence from the Volvox carteri VChR1 gene and the Chlamydomonas reinhardtii ChR1 gene; the first 162 amino acids of ChR1 are fused in-frame to amino acids 102-316 of VChR1, and two point mutations (E122T and E162T) have been introduced in to the coding sequence (PMID:21796121). 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:21796121 and PMID:22179551. For a comparison of C1V1(E122T.E162T) with other neuron activation tools, see PMID:21745635 and PMID:22179551.