UASt regulatory sequences drive expression of a fluorescent biosensor for RhoA activity. The biosensor consists of the Rho-binding domain (RBD) of rhotekin (this specifically binds GTP-bound RhoA), CFP, an unstructured linker, YFP and the full-length RhoA coding region. When the RhoA polypeptide is activated (by binding GTP instead of GDP), the RBD motif can bind it, altering the conformation of the protein and increasing the fluorescence resonance energy transfer (FRET) between the two fluorophores (details from PMID:16547516).