Figure 2. Blue light induced association of optogenetic fusion proteins.

a. Fluorescence lifetime analysis of EGFP component of TCON fusion protein in transiently transfected HeLA cells using FLIM-FRET. Fluorescence lifetime was estimated to be 2.41 ns. b. Blue-light induced change in fluorescence lifetime of EGFP component of TCON fusion in the presence of ECON. Representative HeLA cells co-transfected with TCON and ECON constructs was exposed to 8 mW/cm² of blue light for the indicated time periods. Fluorescence lifetime decreases from 2.43 ns to 2.06 ns over a 5 min exposure to blue light, due to the FRET between EGFP and mCherry, validating the optically induced association of CRY2PHR and CIB1 that are components of TCON and ECON fusions respectively. c. Western blot analysis of co-immunoprecipitated fraction from cells transfected with either TCON, or TCON and ECON treated with presence (+) and in the absence (-) of blue light. Immunoprecipitation was carried out using EGFP antibody, whereas DNMT3A antibody was used for the detection of pulled-down ECON in Western blot. An ECON specific band (ca. 223 kDa) was observed in the blot in the protein fractions of co-transfected illuminated cells (lane-3). In contrast, no anti-DNMT3A Ab specific band was detected in cells transfected with TCON (lane-1) or co-transfected cells lacking light treatment (lane-2). Data shows that blue-light treatment promotes the formation of complexes between TCON and ECON.