Decaging and phosphorylation of S795 stimulates channel activity via promoting phosphorylation of S813. (A) Representative decaging profile for S795S^cage CFTR. Delivery of the 250 ms pulse of LED is indicated as a purple arrowhead. (B) Schematic explanation of whole-dish photochemistry experiment. (C) Left: Western blot using an antibody (CFF ab217) that detects the level of non-phosphorylated S813 motif in the population of CFTR molecules. The lane labeled NO uAA contains lysate from a parallel control transfection without Ser^cage AA present in media and shows the expected lack of full-length channel expression. Right: Western blot quantification and significance comparing three independent experiments for stimulated conditions. P values are from unpaired Student’s t test, and n is the value of experimental replicates indicated in parentheses. (D) Depiction of decaging interval (250 s total, with 40 s before the light pulse) of the 4 S795S^cage experiments. Arrow indicates the location of initial, fast rate of current increase, which varies from prominent (top left, bottom right with fits shown) to subtle (top right, bottom left). Source data are available for this figure: SourceData F5.