UAS regulatory sequences drive expression of the 'MAPPER' (membrane-attached peripheral ER) marker. This marker selectively labels ER (endoplasmic reticulum) - PM (plasma membrane) junctions. It is a fusion protein composed of the signal peptide of the human STIM1 gene (HGNC:11386), GFP, the STIM1 transmembrane domain, an FKBP12-rapamycin binding (FRB) domain that is flanked on both sites by flexible linkers, and the polybasic (PB) motif of the human RIT1 gene (HGNC:10023). The GFP portion is located in the ER lumen, while the Rit PB motif binds to phosphoinositides in the plasma membrane, resulting in a constitutive localization to ER-PM junctions (details from PMID:24183667). The reporter is tagged with mCherry.