Membrane-bound O-acyltransferase involved in the remodeling of glycosylphosphatidylinositol (GPI) anchors. Acts only on GPI-anchored proteins, but not on free GPI lipids. Acts as an acyltransferase for GPI anchors that adds C26 fatty acids to the sn2 position of lyso-PI-containing GPI anchors. PER1 first deacylates, GUP1 subsequently reacylates the anchor lipid, thus replacing a shorter fatty acid (C16:0 or C18:0) by C26:0 (PubMed:16597698, PubMed:18036137). Also involved in lipid metabolism, having profound effects on sphingolipid-sterol-ordered domains integrity and assembly (PubMed:18786505). Together with GUP2, has an influence on the chemical composition of the yeast extracellular matrix (yECM) in yeast multicellular aggregates, such as biofilms and colonies (PubMed:25589358). Involved in cell integrity and apoptosis (PubMed:22617017, PubMed:30184078). Interacts with mitochondrial outer membrane voltage-dependent anion channel (VDAC) POR1. Expressed constitutively. Results in an increase in triglyceride (TG) synthesis with a concomitant decrease in phospholipid (PL) synthesis and exhibits an altered plasma membrane lipid composition (PubMed:10747858). Shows defects in cell wall assembly and stability and abnormal cell wall morphology (PubMed:17042752). Deficient in GPI anchor remodeling, mutant cells only contain the primary, unremodeled phosphatidylinositol (PI) and are unable to attach remodeled PI or ceramides to the anchor (PubMed:16597698). Defective in sterol lipid distribution (PubMed:18786505). Present with 672 molecules/cell in log phase SD medium. Belongs to the membrane-bound acyltransferase family. Was originaly thought to be involved in active uptake of glycerol driven by electrogenic proton symport (PubMed:10931309), but has later been shown to be an acyltransferase and that effects on glycerol transport may be indirect (PubMed:10694878, PubMed:15381122).