In the sixth step of GPI synthesis, a phosphoethanolamine group is transferred from phosphatidylethanolamine onto the first mannose of the GPI precursor. The human protein that catalyzes this reaction was first identified because it could complement a yeast mutant strain defective for GPI synthesis (Gaynor et al. 1999); its specific function in phosphoethanolamine transfer is inferred from functional studies of the homologous mouse protein (Hong et al. 1999). The reaction is annotated here with phosphatidylethanolamine as the donor of the phosphoethanolamine group on the basis of studies in yeast (Imhof et al. 2000).