PhiYFP and PhiYFP-m are the mutants of a natural yellow fluorescent protein from Phialidium sp. (Cnidaria; Hydrozoa; Hydroida; Leptomedusae; Campanulariidae) [Shagin et al., 2004].

Phi-Yellow proteins have excitation/emission maxima at 525 and 537 nm, respectively. They exhibit lower brightness and maturation rate than TurboYFP, but are more suitable for generation of stably transfected cell lines. The emission wavelength of these proteins is ideally positioned between those of green and red fluorescent proteins, allowing easy separation of these fluorescent tags by flow cytometry using common channels of detection and a single laser excitation line.