Tag:2xFYVE consists of two copies of the FYVE finger domain of the mouse HGF-regulated tyrosine kinase substrate (Hgs) gene (MGI:MGI:104681), separated by a QCQGS linker. Tag:2xFYVE binds specifically and with high affinity to phosphatidylinositol-3-phosphate in vitro and in vivo (PMID:10970851). This tool can thus be used to monitor the distribution of phosphatidylinositol-3-phosphate within a cell, if fused to an appropriate reporter protein, or to target a tagged protein to a particular subcellular localization via phosphatidylinositol-3-phosphate binding. For a review of the properties of Tag:2xFYVE and a comparison with other genetically encoded lipid biosensors, see PMID:29953345.