UAS regulatory sequences drive expression of the 'psMEK1tight' photoswitchable kinase. psMEK1tight consists of Maur\MEK1 with two phosphomimetic mutations in the active loop (S218D and S222D), resulting in a constitutively active enzyme, and into which two copies of pdDronpa1.2 have been inserted: one after the N-terminal substrate docking site (insertion after codon 60), and the other in the FG loop (insertion after codon 304). The two pdDronpa1.2 moieties reversibly cage the Maur\MEK1 active site; when the two pdDronpa1.2 domains form a dimer, they sterically hinder access to the Maur\MEK1 active site, but when the pdDronpa1.2 domains dissociate, the active site of the constitutively active Maur\MEK1 is exposed. 'psMEK1tight' can be reversibly switched between the two conformations in a light-regulated manner: illumination with light of wavelength 400nm favours the closed conformation (dimerized pdDronpa1.2 moieties), while light of wavelength 500nm favors the open conformation in which the Maur\MEK1 active site is exposed (details from PMID:28232577).