The cytoFLARE1.0::lexA::VP16 driver encodes a conditional transcriptional activator that is designed to be used together with the TEVp(S153N)::CaM protease in the 'cytoFLARE' system and which requires both blue light stimulation and high Ca[2+] to be activated. cytoFLARE1.0::lexA::VP16 is a fusion protein composed of 'ER[T2]' (a mutant estrogen ligand-binding domain), 'MK2' (a calmodulin-binding peptide), 'hLOV1' (a hybrid LOV1 domain), a TEVp protease target site, and the lexA::VP16 driver. The ER[T2] sequence results in the cytoFLARE1.0::lexA::VP16 protein being located in the cytosol and in the absence of blue light, the hLOV1 domain cages the TEVp protease target site. Stimulation by blue light results in a conformational change in the hLOV1 domain of cytoFLARE1.0::lexA::VP16 that uncages the TEVp protease target site, while in the presence of high Ca[2+], the calmodulin sequence in the TEVp(S153N)::CaM protease can bind the MK2 peptide of cytoFLARE1.0::lexA::VP16, bringing the protease in close proximity to its target site. Thus, in the presence of both blue light and high Ca[2+] levels, the TEVp(S153N)::CaM protease can cleave the TEVp protease target site in cytoFLARE1.0::lexA::VP16, releasing the lexA::VP16 driver which can then translocate to the nucleus and activate transcription of a transgene expressed under the control of lexAop regulatory sequences (FBrf0262143).