Diacylglycerol kinase (EC:2.7.1.107) (DAGK) is an enzyme that catalyses the formation of phosphatidic acid from diacylglycerol and ATP, an important step in phospholipid biosynthesis. In bacteria DAGK is very small (13 to 15 kD) membrane protein which seems to contain three transmembrane domains [1]. The best conserved region, is a stretch of 12 residues which are located in a cytoplasmic loop between the second and third transmembrane domains.