GUP1 is a 504 amino acid multipass membrane protein of the endoplasmic reticulum that functions as a membrane bound O-acyltransferase. With specific expression in heart, GUP1 negatively regulates amino-terminal palmitoylation of Shh by HHAT, a protein that is required for Shh signaling. Deletion of the gene encoding GUP1 results in higher sensibility to specific sphinogolipid biosynthesis inhibitors and resistance to ergosterol biosynthesis inhibitors, indicating that GUP1 is an essential component in lipid metabolism. Also, GUP1 also seems to be important for cell wall assembly and stability due to evidence in Saccharomyces cerevisiae GUP1 mutants, which exhibit altered plasma membrane lipid composition and membrane potential.