UASp regulatory sequences drive expression of a mitochondria-ER contact site (MERCs) quantification construct based on a split-GFP-based contact site sensor (SPLICS) with an 45-50 nm range. The UASp sequences drive expression of two open reading frames separated by a P2A peptide (to ensure separate translation of the two ORFs and equimolar amounts of the two expressed proteins). The first ORF encodes a protein composed of an ER membrane targeting sequence, a 'long' spacer of 146 amino acids, and the spGFP11 split fragment. The second ORF encodes the spGFP1-10 split fragment tagged with sequence that anchors it to the mitochondrial outer membrane. Where the ER and mitochondrial outer membranes are in close proximity, the spGFP1-10 and spGFP11 moieties can self-assemble to reconstitute a functional sfGFP protein, resulting in fluorescent puncta (details from PMID:29229997).