smo regulatory sequences drive expression of the smo coding sequence in which amino acids 757-915 of the cytoplasmic tail have been replaced by a conformation-sensitive circularly permutated yellow fluorescent protein (cpYFP). This protein is designed to act as a fluorescent sensor of phosphorylation of the smo tail; in the absence of phosphorylation the closed conformation of the smo tail should keep the cpYFP core in a non-fluorescent conformation, whereas phosphorylation of the SAID domain should allow the cpYFP core to relax into a fluorescent conformation.